Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Reexamination Certificate
2002-09-09
2004-05-04
Kamen, Noah P. (Department: 3726)
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
C123S0730PP
Reexamination Certificate
active
06729274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a cylinder for an internal combustion engine such as a small air-cooled two-stroke gasoline engine which is suited for use in a portable power working machine.
2. Description of the Related Art
One typical example of a cylinder for a small air-cooled two-stroke gasoline engine currently employed in a portable power working machine is illustrated in
FIGS. 1 and 2
. Specifically,
FIG. 1
shows a longitudinal sectional view of a cylinder
1
, and
FIG. 2
shows a cross-sectional view of the cylinder, wherein the air-inlet and exhaust ports thereof are shown as being formed at the same level with each other for the convenience of illustration. The cylinder
1
shown in this example is generally formed of an aluminum alloy. The cylinder
1
includes an integral body consisting of a main body
2
having a cylinder bore
9
for allowing a piston
20
to be fitted therein and a pair of columnar expanded portions
2
a
disposed opposite to each other. The cylinder further includes a head portion
3
provided with a so-called squish dome-shaped combustion chamber
4
. The main body
2
is provided, all over the outer wall thereof, with a large number of cooling fins
19
. Further, the head portion
3
is provided with an internal thread
18
for mounting an ignition plug.
The cylinder bore
9
is provided with an air-inlet port
5
and also with an exhaust port
6
, which are designed to be closed and opened by the movement of the piston
20
. The air-inlet port
5
and the exhaust port
6
are disposed opposite to each other in such a manner that they are offset or dislocated level-wise from each other. The columnar expanded portions
2
a
are respectively provided therein with a hollow scavenging passageway
7
having an inner wall
10
of predetermined thickness. Each hollow scavenging passageway
7
is spaced away from the air-inlet port
5
and the exhaust port
6
by an angle of 90 degrees in the circumferential direction of the cylinder bore
9
. These scavenging passageways
7
are respectively provided, at a downstream end portion (upper end portion) thereof, with a scavenging port
8
which is inclined somewhat upward, i.e., in the direction away from where the exhaust port
6
of the cylinder bore
9
is located. The two scavenging ports
8
are also designed so that they are opened and closed by the movement of the piston.
The cylinder
1
mentioned above is a so-called binary fluid scavenging type cylinder where the two scavenging ports
8
are symmetrically formed with respect to the longitudinal section F taken along the middle of the exhaust port
6
. However, a so-called quaternary fluid scavenging type cylinder having an additional pair of scavenging ports (two pairs in total) is also known.
In addition to the hollow scavenging passageway provided with the inner wall
10
as shown in
FIG. 1
, one type of scavenging passageway has no inner wall (the side facing the cylinder bore is opened). Another kind of scavenging passageway has a lower portion with an opening extending along the length of the scavenging passageway while leaving a half-wall at an upper portion thereof. This enables the air-fuel mixture that has been introduced into the scavenging port from the crank chamber via the scavenging passageway to be contacted with the skirt portion of the piston.
If a cylinder provided in particular with an inner wall-attached (including a half-wall-attached) hollow scavenging passageway among the aforementioned cylinders for a two-stroke internal combustion engine is to be manufactured by means of a die casting method such as a high-pressure die casting method which enables cast moldings of high dimensional precision to be produced at low cost, the scavenging port portion of the scavenging passageway is inevitably formed into an undercut portion. However, since a collapsible core cannot be employed under a high pressure, a raw cylinder body
1
′ is cast-molded by means of the high-pressure die casting method, resulting in the scavenging port portion (constituting an undercut portion)
12
thereof being left closed as shown in
FIGS. 3 and 4
. Therefore, the closed scavenging port portion
12
is subsequently cut out (or opened) by mechanical means such as cutting work, electric discharge machining, laser beam machining, etc. For reference,
FIGS. 5 and 6
show the closed scavenging port portion
12
to be cut out for forming one of the scavenging ports
8
which is located on the left side in
FIGS. 3 and 4
, wherein this left side scavenging port portion
12
is depicted as an enlarged view with the hatching thereof being densitied and reversed in direction.
However, the aforementioned method of cutting out the closed scavenging port portion
12
by mechanical means such as cutting work, electric discharge machining, laser beam machining, etc. for forming the scavenging ports
8
after the casting of the raw cylinder body has the following problems. Namely, as shown in
FIGS. 9 and 10
, both illustrating enlarged views of the peripheral region of the left side scavenging port
8
, when cutting out the closed scavenging port portion
12
by mechanical means such as cutting work, electric discharge machining, laser beam machining, etc. for forming the scavenging ports
8
, this cut-out work is required to be performed in such a manner that the inner surface of each of the scavenging ports
8
is made flush with the plane of each of the inner surfaces
8
a
,
8
c
and
8
d
of the hollow scavenging passageways which were previously formed contiguous to each of the closed scavenging port portions
12
. Therefore, if there is even a slight deviation in the location of working tools, working direction or the location of the working portion (the location of the scavenging port
8
), a step portion Da, Dc or Dd would be generated at the scavenging ports
8
. If there is such a step portion Da, Dc or Dd at the scavenging ports
8
, it would become a source of scavenging resistance, turbulence of scavenging gas flow, increased mechanical loss, or deterioration in engine performance such as the deterioration in combustibility or in purification of exhaust gas.
It is desirable to prevent the generation of the aforementioned step portions Da, Dc and Dd. It is further desirable to avoid the enhanced precision positioning of the working tools as well as the working location required to a great extent, which results in an increase in manufacturing cost. Indeed, it is impossible to completely obviate the generation of the aforementioned step portion Da, Dc or Dd.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made to overcome the aforementioned problems. Therefore, an object of the present invention is to provide a method for manufacturing a cylinder for an internal combustion engine that avoids the generation of a step portion at the scavenging port without needing to enhance the precision of the positioning of the working tools or the working location in the working process. A raw cylinder body is cast-molded with its scavenging port portion being left closed. Subsequently, this closed scavenging port portion is cut out (or opened) by means of cutting work, electric discharge machining, laser beam machining, etc.
The present invention provides a method of manufacturing a cylinder for an internal combustion engine, wherein the cylinder is provided with an inner wall-attached hollow scavenging passageway having a scavenging port to be opened and closed by the movement of piston. The method essentially comprises two steps. The first step comprises cast-molding a raw cylinder body with its scavenging port portion being left closed. The second step comprises cutting out (or opening) the closed scavenging port portion by means of cutting work, electric discharge machining, laser beam machining, etc. to form the scavenging port.
The step of cutting out the closed scavenging port portion is performed by widening the cylinder bore side of the closed scavengin
Fujisawa Takashi
Inokuma Masahiro
Matuura Fujihiro
Baker & Botts L.L.P.
Kamen Noah P.
Kioritz & Corporation
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