Internal-combustion engines – Two-cycle – Rear compression
Reexamination Certificate
2001-10-15
2002-12-24
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Two-cycle
Rear compression
C123S0730AE, C123S0650WA
Reexamination Certificate
active
06497204
ABSTRACT:
The present invention relates to a stratified scavenging two-stroke cycle engine, and more particularly to a piston valve type stratified scavenging two-stroke cycle engine which separately sucks an air-fuel mixture and leading air for scavenging.
BACKGROUND ART
Conventionally, as an example of a piston valve type stratified scavenging two-stroke cycle engine having a piston groove for connecting a leading air sucking port and a scavenging port in an outer peripheral portion of a piston, there has been known a structure which is disclosed in International Laid-Open WO 98/57053.
FIGS. 12 and 13
show one structural embodiment of the stratified scavenging two-stroke cycle engine described in WO 98/57053. A piston
4
is provided so as to be slidably and in a sealing manner inserted within a cylinder
3
. The piston
4
is connected to a crank
5
within a crank chamber
11
via a connecting, rod
6
. A space portion, in which a capacity above the piston
4
within the cylinder
3
changes, forms a cylinder chamber
10
. Two scavenging flow passages
20
and
20
, communicating the cylinder chamber
10
with the crank chamber
11
, are provided on opposite side surfaces of the cylinder
3
. The respective scavenging flow passages
20
and
20
are open as scavenging ports
21
and
21
to the cylinder chamber
10
. An exhaust port is provided in a side of the cylinder
3
adjacent a top dead center side of the piston
4
at a position above the scavenging ports
21
and
21
in an axial direction of the cylinder
3
. Further, an air-fuel mixture suction port
23
and leading air suction ports
24
and
24
, disposed adjacent opposite sides of the air-fuel mixture port
23
, are provided on an inner peripheral surface of the cylinder
3
. A through hole
31
is provided in a lower portion of the piston
4
. Piston grooves
25
and
25
, respectively communicating the leading air suction ports
24
and
24
with the scavenging ports
21
and
21
in correspondence to a vertical motion of the piston
4
, are provided in right and left outer peripheral surfaces with respect to the through hole
31
.
As shown in
FIG. 14
, in order to prevent the leading air suction ports
24
and
24
and the air-fuel mixture suction port
23
from communicating with each other throughout all of the strokes of the piston
4
, the interval between the two leading air suction ports
24
and
24
, that is, the interval K between the piston grooves
25
and
25
, is set to be larger than the width M of the air-fuel mixture suction port
23
.
In the stratified scavenging two-stroke cycle engine having the structure mentioned above, when the piston
4
moves upwardly from a bottom dead center, the pressure of the crank chamber
11
starts reducing and the pressure of the cylinder chamber
10
starts increasing, so that each scavenging port
21
and the exhaust port
22
are sequentially closed. Further, at this time, as shown in
FIG. 14
, the leading air suction ports
24
and
24
are in a state of being connected to the scavenging flow passages
20
and
20
via the piston grooves
25
and
25
and the scavenging ports
21
and
21
at a position close to and below the top dead center, and the air-fuel mixture suction port
23
is opened so as to become in a state of being connected to the crank chamber
11
via the through hole
31
. Accordingly, the air is sucked within the crank chamber
11
from the leading air suction ports
24
and
24
via the scavenging flow passages
20
and
20
. At this time, inner portions of the scavenging flow passages
20
and
20
become in a state of being full of the air.
When the piston further moves upwardly and the piston
4
reaches a point close to the top dead center, the air-fuel mixture within the cylinder chamber
10
is ignited and exploded, whereby the piston
4
starts moving downwardly. Accordingly, the pressure of the crank chamber
11
starts increasing, the piston grooves
25
and
25
become in a state of being shut off from the leading air suction ports
24
and
24
and the scavenging ports
21
and
21
, and the air-fuel mixture suction port
23
becomes in a state of being closed by the piston
4
, so that the pressure within the crank chamber
11
increases.
In the middle of the downward movement of the piston
4
, the exhaust port
22
and the scavenging ports
21
and
21
become sequentially in a state of being opened to the cylinder chamber
10
, and combustion gas is at first discharged from the exhaust port
22
. Next, the air stored within the scavenging flow passages
20
and
20
is injected into the cylinder chamber
10
from the scavenging ports
21
and
21
due to the increased pressure within the crank chamber
11
. Accordingly, the combustion gas left within the cylinder chamber
10
is expelled via the exhaust port
22
and a muffler (not shown) into atmospheric air. Next, the air-fuel mixture within the crank chamber
11
is charged into the cylinder chamber
10
via the scavenging flow passages
20
and
20
and the scavenging ports
21
and
21
.
Further, the piston
4
starts moving upwardly from the bottom dead center, whereby the pressure within the crank chamber
11
starts reducing, and each scavenging port
21
and the exhaust port
22
are sequentially closed, so that the cycle mentioned above is again repeated.
Further, conventionally, an air control valve for adjusting an air supply amount is provided in an upstream side of the leading air suction port. As one embodiment thereof, there has been known Japanese Utility Model Publication No. 55-4518.
FIG. 15
shows one structural embodiment of a stratified scavenging two-stroke cycle engine described in Japanese Utility Model Publication No. 55-4518, and
FIG. 16
is a cross sectional view along a line
16
—
16
in FIG.
15
. The same reference numerals are attached to the same elements as those in
FIG. 12
, a description thereof will be omitted, and a description will be given only of different parts. A carburetor
50
, having a suction air throttle valve
51
, is provided in the air-fuel mixture suction port
23
, which is open to the crank chamber
11
. A two-forked branch pipe
61
, attached to an air supply pipe
60
and branched into two air supply passages
62
and
62
, is attached to the cylinder
3
. The air supply passages
62
and
62
of the branch pipe
61
are communicated with the scavenging ports
21
and
21
, which are open to the cylinder chamber
10
. Check valves
65
and
65
are respectively provided in the air supply passages
62
and
62
. An air control valve
63
, having a butterfly type variable valve
64
, is provided in the air supply pipe
60
. The variable valve
64
is structured such as to be connected to the suction air throttle valve
51
of the carburetor
50
by a rod
52
so as to interlock therewith. An exhaust port
22
is provided on a surface of the cylinder
3
opposite from the air supply pipe
60
.
In the structure mentioned above, when the piston
4
starts moving upwardly from the bottom dead center, the air is supplied to the scavenging ports
21
and
21
from the air supply pipe
60
via the air supply passages
62
and
62
of the branch pipe
61
. Then, the amount of air is adjusted by the air control valve
63
. The air control valve
63
is operated interlocking with the suction air throttle valve
51
in the carburetor
50
and is set so that 0 or a small amount of air is supplied at a time when the engine is under idling or under a low load operation, and an amount of air corresponding to an operation condition is supplied at the other operation times.
However, in the structure disclosed in WO 98/57053 mentioned above, the following problems are generated.
In order to increase a suction efficiency of the air-fuel mixture, it is necessary to form the air-fuel mixture suction port
23
to be equal to or more than a predetermined area. Further, in the same manner, in order to increase a suction efficiency and a scavenging efficiency of the leading air, it is necessary to form the scavenging ports
21
and
21
and th
Miyazaki Hiroshi
Otsuji Takamasa
Kamen Noah P.
Komatsu Zenoah & Co.
Sidley Austin Brown & Wood LLP
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