U.S. patent application number 10/870809 was filed with the patent office on 2004-12-30 for method for manufacturing a cylinder for internal combustion engine.
This patent application is currently assigned to Kioritz Corporation. Invention is credited to Kocha, Masaharu, Matsumoto, Kuninori, Matuura, Fujihiro.
Application Number | 20040261971 10/870809 |
Document ID | / |
Family ID | 33535206 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040261971 |
Kind Code |
A1 |
Matsumoto, Kuninori ; et
al. |
December 30, 2004 |
Method for manufacturing a cylinder for internal combustion
engine
Abstract
A method is provided for manufacturing a cylinder for an
internal combustion engine, which makes it possible not only to
manufacture the cylinder by a high-pressure die casting method at
low cost and in high precision, but also to prevent relative
misalignment among the scavenging port, suction port and exhaust
port of the cylinder. This method is characterized by the steps of:
preparing a cylinder liner made of an aluminum alloy pipe and
provided with the scavenging port, and a bore-core die as well as
cores for scavenging ducts both being uncollapsible and configured
so as not to intrude into the scavenging ports; setting the
cylinder liner in place in the bore-core die; and casting, by means
of metal mold casting method, an aluminum alloy onto the outer
peripheral surface of the cylinder liner to thereby mold a main
body of the cylinder.
Inventors: |
Matsumoto, Kuninori;
(Kanagawa, JP) ; Kocha, Masaharu; (Saitama,
JP) ; Matuura, Fujihiro; (Kanagawa, JP) |
Correspondence
Address: |
BAKER & BOTTS
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
|
Assignee: |
Kioritz Corporation
Tokyo
JP
|
Family ID: |
33535206 |
Appl. No.: |
10/870809 |
Filed: |
June 17, 2004 |
Current U.S.
Class: |
164/98 |
Current CPC
Class: |
B22D 19/0009
20130101 |
Class at
Publication: |
164/098 |
International
Class: |
B22D 019/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2003 |
JP |
2003-181592 |
Claims
What is claimed is:
1. A manufacturing method of a cylinder for an internal combustion
engine provided with an inner wall-attached hollow scavenging duct
having a scavenging port to be opened and closed by the movement of
a piston, the method comprising the steps of: preparing a cylinder
liner made of an aluminum alloy pipe and provided with the
scavenging port, and a bore-core die as well as a core for
scavenging duct both being uncollapsible and configured so as not
to intrude into the scavenging port; setting the cylinder liner in
place in the bore-core die; and casting, by means of a metal mold
casting method, an aluminum alloy as a raw material onto the outer
peripheral surface of the cylinder liner to thereby mold a main
body of the cylinder.
2. The manufacturing method according to claim 1, wherein said
cylinder liner is provided in advance with a suction port as well
as an exhaust port in addition to the scavenging port.
3. The manufacturing method according to claim 1, which further
comprises a step of providing melt intrusion prevention means for
preventing melt from entering into the scavenging port on the
occasion of metal mold casting.
4. The manufacturing method according to claim 3, wherein said melt
intrusion prevention means is configured so as to prevent the
generation of a step portion between the scavenging port and the
scavenging duct of the main body of the cylinder.
5. The manufacturing method according to claim 3, wherein said melt
intrusion prevention means comprises a blocking member removably
attached to the scavenging port.
6. The manufacturing method according to claim 3, wherein said melt
intrusion prevention means comprises a thick-walled portion or a
rib portion configured to be in contact with the core for the
scavenging duct and disposed all around an outer periphery of the
cylinder liner excluding a lower side of the scavenging port in a
manner to prevent the generation of a step portion relative to the
scavenging port.
7. The manufacturing method according to claim 1, wherein a
chamfered portion is formed in advance on an inner periphery of an
opening such as the scavenging port formed in the cylinder
liner.
8. The manufacturing method according to claim 1, wherein a portion
of the outer peripheral surface of the cylinder liner, which
contacts with the main body of the cylinder, is coated in advance
with a metal having a lower melting point than that of the aluminum
alloy.
9. The manufacturing method according to claim 1 further comprising
preventing the generation of a step portion between the scavenging
port and the scavenging duct of the main body of the cylinder.
10. A cylinder for an internal combustion engine provided with an
inner wall-attached hollow scavenging duct having a scavenging port
to be opened and closed by the movement of a piston, the cylinder
being manufactured by the steps of: preparing a cylinder liner made
of an aluminum alloy pipe and provided with the scavenging port,
and a bore-core die as well as a core for scavenging duct-both
being uncollapsible and configured so as not to intrude into the
scavenging port; setting the cylinder liner in place in the
bore-core die; and casting, by means of a metal mold casting
method, an aluminum alloy as a raw material onto the outer
peripheral surface of the cylinder liner to thereby mold a main
body of the cylinder.
11. The cylinder according to claim 10, wherein in the
manufacturing of the cylinder, said cylinder liner is provided in
advance with a suction port as well as an exhaust port in addition
to the scavenging port.
12. The cylinder according to claim 10, wherein the manufacturing
of the cylinder further comprises a step of providing melt
intrusion prevention means for preventing melt from entering into
the scavenging port on the occasion of metal mold casting.
13. The cylinder according to claim 12, wherein said melt intrusion
prevention means in manufacturing the cylinder is configured so as
to prevent the generation of a step portion between the scavenging
port and the scavenging duct of the main body of the cylinder.
14. The cylinder according to claim 12, wherein said melt intrusion
prevention means in manufacturing the cylinder comprises a blocking
member removably attached to the scavenging port.
15. The cylinder according to claim 12, wherein said melt intrusion
prevention means in manufacturing the cylinder comprises a
thick-walled portion or a rib portion configured to be in contact
with the core for the scavenging duct and disposed all around an
outer periphery of the cylinder liner excluding a lower side of the
scavenging port in a manner to prevent the generation of a step
portion relative to the scavenging port.
16. The cylinder according to claim 10, wherein in manufacturing
the cylinder, a chamfered portion is formed in advance on an inner
periphery of an opening such as the scavenging port formed in the
cylinder liner.
17. The cylinder according to claim 10, wherein a portion of the
outer peripheral surface of the cylinder liner, which contacts with
the main body of the cylinder, is coated in advance with a metal
having a lower melting point than that of the aluminum alloy.
18. The cylinder according to claim 10, wherein the manufacturing
of the cylinder further comprises preventing the generation of a
step portion between the scavenging port and the scavenging duct of
the main body of the cylinder.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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. In particular, the present
invention relates to a manufacturing method of the cylinder for an
internal combustion engine to be used, for example, in a portable
power working machine, the manufacturing method enabling an
undercut portion of the cylinder such as a scavenging port to be
rationally formed in the manufacture of the cylinder by means of a
die casting method such as a high-pressure die casting method.
[0003] 2. Description of the Related Art
[0004] The cylinder of a small air-cooled two-stroke gasoline
engine to be used in a portable power working machine is, as seen
for instance from JP Laid-open Patent Publication (Kokai) No.
58-155114 (1983), generally formed of an aluminum alloy and
constituted by an integral body consisting of a main body having a
cylinder bore formed therein for allowing a piston to be fitted
therein, and a head portion having a squish dome-shaped combustion
chamber formed therein, and by a large number of cooling fins
projecting from all over the outer wall of the integral body.
[0005] The cylinder bore is provided with a suction port and also
with an exhaust port, both of which are designed to be closed or
opened by the movement of the piston, these suction port and
exhaust port being arranged so as to face each other in an off-set
manner so that they differ in level from each other. A plurality of
hollow scavenging ducts, each being displaced away from these
suction port and exhaust port by an angle of 90 degrees and having
an inner wall of predetermined thickness, are formed along with the
cylinder bore. The downstream end portion (upper end portion) of
each hollow scavenging duct is constituted by a scavenging port,
thereby providing a pair of scavenging ports which are disposed
opposite to each other and designed to be opened and closed by the
piston, these scavenging ports being inclined somewhat upward and
directed in the direction opposite to the exhaust port of the
cylinder bore.
[0006] The cylinder disclosed in the aforementioned JP Laid-open
Patent Publication (Kokai) No. 58-155114 is a so-called binary
fluid scavenging type cylinder where a pair of scavenging ports are
symmetrically formed with respect to the longitudinal section taken
along the middle of the exhaust port. Additionally, a so-called
quaternary fluid scavenging type cylinder where a pair of
scavenging ports are additionally provided therewith (two pairs of
scavenging ports in total) is also known.
[0007] As for the type of the scavenging duct, there are known a
hollow scavenging duct provided with an inner wall as shown in the
aforementioned JP Laid-open Patent Publication (Kokai) No.
58-155114, a scavenging duct having no inner wall (the side facing
the cylinder bore is opened), and, as shown in the aforementioned
JP Laid-open Patent Publication (Kokai) No. 2000-34927, a
scavenging duct provided with a half-wall and featured in that it
is provided at a lower portion thereof with an opening extending in
the longitudinal direction of the scavenging duct while leaving a
half-wall having a predetermined thickness at an upper portion
thereof so as to allow an air-fuel mixture introduced through the
scavenging duct into the scavenging port from the crank chamber to
be directly contacted with a skirt portion of the piston.
[0008] In the manufacture of a cylinder provided with an inner
wall-attached (or a half-wall-attached) hollow scavenging duct, in
particular among the aforementioned cylinders for a two-stroke
internal combustion engine, by means of a die casting method such
as a high-pressure die casting method which enables the cast
molding of high dimensional precision at low cost, the scavenging
port portion of the scavenging duct which constitutes an undercut
portion has been generally created by the following procedures.
Namely, since a collapsible core for forming the cylinder bore
portion cannot be employed under a high pressure, a raw cylinder
body is cast-molded at first in such a manner that the scavenging
port portion (constituting an undercut portion) thereof is left
closed, and thereafter, this closed scavenging port portion is cut
out by mechanical means (see JP Laid-open Patent Publication
(Kokai) No. 58-155114 (1983)).
[0009] There is a problem however in the aforementioned method to
cut out a scavenging port by mechanical means after the casting of
raw cylinder body. Namely, since the space for allowing a cutting
tool to be inserted into a working portion is very narrow, it is
very difficult to perform the mechanical working and to enhance the
processing accuracy of the scavenging port. In this case, since the
performance of a two-stroke internal combustion engine is greatly
influenced by the size and configuration of the scavenging port as
well as by the processing accuracy thereof, this problem associated
with the aforementioned mechanical working is very important.
[0010] It may be conceivable to manufacture a cylinder provided
with an inner wall-attached hollow scavenging duct by means of a
die casting method employing an insert core to be inserted into the
scavenging port portion. In this case however, since part of the
insert core is left in the cast product, the heat conductivity
thereof is deteriorated and at the same time, various problems such
as the deformation or peeling due to the remaining insert core may
occur.
[0011] Meanwhile, as for the manufacturing method of a cylinder for
an internal combustion engine, there is also known, as described
above in JP Patent Publication No. 52-47091 (1977) and JP Laid-open
Patent Publication (Kokai) No. 1-309774 (1989), a method wherein a
cylinder liner (sleeve) provided in advance with a scavenging port,
a suction port and an exhaust port is manufactured (cast) at first
by making use of a ferrous material, and then, a main body of
cylinder is cast by means of metal mold casting on the outer
peripheral surface of the cylinder liner by making use of an
aluminum alloy as a raw material.
[0012] However, the cylinders that can be manufactured by the
methods shown in JP Patent Publication No. 52-47091 and JP
Laid-open Patent Publication No. 1-309774 are accompanied with
problems that since the cylinder liner portion is formed of a
ferric cast article, a mold which is exclusively designed for the
manufacture of the cylinder liner portion is required to be
separately prepared thus resulting in an increase of manufacturing
cost, and that since the cylinder liner is formed of a material
which differs in thermal expansion coefficient as well as in
thermal conductivity from those of the material from which the main
body of the cylinder is formed, there are significant possibilities
of generating problems such as peeling between them, a step portion
around the opening such as scavenging port or misalignment between
them.
[0013] Further, according to the manufacturing method described in
JP Patent Publication No. 52-47091, the scavenging port portion,
suction port portion and exhaust port portion of the cylinder liner
are all constructed so as to protrude outward from the cylindrical
portion of the cylinder liner in order to prevent a melt from
entering into the interior (through opened portions) of the
cylinder liner on the occasion of the casting the main body of the
cylinder, so that a mold, an insert core, etc. each having a
complicated configuration, are required to be employed, thereby
further increasing the manufacturing cost of the cylinder.
[0014] On the other hand, according to the manufacturing method
described in JP Laid-open Patent Publication No. 1-309774, since it
is required to employ a collapsible core as insert cores for
forming a bore-core die, each of the openings and each of the
ducts, it is impossible to apply this manufacturing method to the
manufacture of the cylinder by making use of a die casting method
such as a high-pressure die casting method which enables the cast
molding of high dimensional precision at low cost.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention has been made to overcome the
aforementioned problems accompanied with the prior art, and
therefore an object of the present invention is to provide a method
for manufacturing a cylinder for an internal combustion engine,
which not only makes it possible to manufacture the cylinder by
means of a die casting method such as a high-pressure die casting
method at low cost and in high precision without raising problems
such as the deterioration of heat conductivity, and the deformation
or peeling of the cylinder, but also makes it possible to prevent
relative misalignment among the scavenging port, the suction port
and the exhaust port of the cylinder to be obtained.
[0016] With a view to realize the aforementioned object, the
present invention provides a manufacturing method of a cylinder for
an internal combustion engine provided with an inner wall-attached
hollow scavenging duct having a scavenging port to be opened and
closed by the movement of a piston, the method being characterized
by the steps of: preparing a cylinder liner made of an aluminum
alloy pipe and provided with the scavenging port, and a bore-core
die as well as a core for scavenging duct both being uncollapsible
and configured so as not to intrude into the scavenging port;
setting the cylinder liner in place in the bore-core die; and
casting, by means of metal mold casting method, an aluminum alloy
as a raw material onto the outer peripheral surface of the cylinder
liner to thereby mold a main body of the cylinder.
[0017] In a preferable embodiment, the cylinder liner is provided
in advance with a suction port as well as an exhaust port in
addition to the scavenging port.
[0018] In another preferable embodiment, melt intrusion prevention
means is provided for preventing melt from entering into the
scavenging port on the occasion of metal mold casting. Preferably,
the melt intrusion prevention means is designed so as to prevent
the generation of a step portion between the scavenging port and
the scavenging duct of the main body of cylinder. As a preferable
embodiment of the melt intrusion prevention means, a blocking
member is employed and removably attached to the scavenging
port.
[0019] As another preferable embodiment of the melt intrusion
prevention means, a thick-walled portion or a rib portion to be
face-contacted with the core for the scavenging duct is provided
around an outer periphery of the cylinder liner excluding a lower
side of the scavenging port in a manner to prevent the generation
of a step portion relative to the scavenging port.
[0020] In a preferable embodiment, a chamfered portion is formed in
advance on an inner periphery of an opening such as the scavenging
port formed in the cylinder liner.
[0021] In another preferable embodiment, a portion of the outer
peripheral surface of the cylinder liner, which contacts with the
main body of the cylinder, is coated in advance with a metal having
a lower melting point than that of the aluminum alloy.
[0022] According to the aforementioned preferable embodiments of
the method of manufacturing a cylinder for an internal combustion
engine which is constructed as described above, due to the
employment of the die and the insert core both being uncollapsible,
it is possible to utilize a high-pressure die casting method which
enables one to obtain a cast article of high dimensional precision
at low cost. Additionally, since the cylinder liner is provided in
advance with a scavenging port, a suction port and an exhaust port,
it is possible to manufacture the cylinder with higher precision
and at lower cost as compared with the conventional manufacturing
methods such as the method wherein the port portions such as the
scavenging port are cut out by mechanical working after die casting
or the method wherein an insert core to be inserted into the
scavenging port portion is used. At the same time, it is now
possible to obviate the aforementioned problems of the
deterioration of heat conductivity as well as the deformation or
peeling of these port portions due to the remnant of the insert
core in the cast article (cylinder).
[0023] Additionally, since the cylinder liner is formed by making
use of an aluminum alloy pipe, the cylinder liner can be
manufactured at a lower cost as compared with the case where a
liner produced through casting is employed. Further, since the
cylinder liner is formed of the same material (aluminum alloy) as
that of the main body of the cylinder, there is no possibility of
generating any difference in thermal expansion coefficient as well
as in thermal conductivity, thereby making it possible to inhibit
the generation of problems such as peeling between them, a step
portion around the opening such as scavenging port or misalignment
between them. Further, since the cylinder liner and the main body
of the cylinder are formed of the same material with each other, it
is advantageous in terms of recycle (re-use) of materials.
[0024] Furthermore, since the cylinder liner is provided in advance
with these scavenging port portion, suction port portion and
exhaust port portion, there is little possibility of generating
relative misalignment among these port portions, thus uniquely
determining the positions of the scavenging port, the suction port
and the exhaust port, thereby making it possible to obtain the
cylinder excellent in dimensional precision and preventing the
generation of relative mismatching among the scavenging port, the
suction port and the exhaust port with regard to the timing of
opening and closing to be effected by the piston.
[0025] Since the melt intrusion prevention means is provided for
preventing melt from entering into the scavenging port on the
occasion of metal mold casting, it is now possible to reliably
prevent the melt from entering into the scavenging port, thus
making it possible to save the time and labor required for the
finish working of the cylinder such as deflashing work after the
casting thereof. Moreover, since the melt intrusion prevention
means is designed so as to prevent the generation of a step portion
between the scavenging port and the scavenging duct of the main
body of the cylinder, it is possible to prevent the generation of
turbulence in the scavenging gas flow to be injected in the
combustion chamber disposed over the top of piston.
[0026] Further, when the inner peripheral edge portion of the
opening such as the scavenging port, etc. that has been formed in
advance in the cylinder liner is preliminarily chamfered, finish
chamfering work after casting can be easily performed.
[0027] Further, when a specific region in the outer peripheral
surface of the cylinder liner, which is designed to be contacted
with the main body of the cylinder is coated (through
electroplating, nonelectrolytic plating, ion plating, etc.) with a
metal (for example, zinc, tin, etc.) having a lower melting point
than that of the aluminum alloy, the metal thus coated is enabled
to melt on the occasion of casting, resulting in enhancement of
adhesion between the cylinder liner and the main body of the
cylinder. As a result, the heat conduction from the cylinder liner
to the main body of the cylinder can be enhanced, thus improving
the heat dissipation and cooling properties of the cylinder.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0028] FIG. 1 is a longitudinal sectional view of the scavenging
port portion, as a cylinder liner to be used in one embodiment of
the manufacturing method of cylinder for internal combustion engine
according to the present invention is set in position in a
bore-core die as well as in the core for the scavenging duct;
[0029] FIG. 2 is a longitudinal sectional view of the suction port
portion and the exhaust port portion, as a cylinder liner to be
used in one embodiment of the manufacturing method of cylinder for
internal combustion engine according to the present invention is
set in position in a bore-core die as well as in the core for the
scavenging duct;
[0030] FIG. 3 is a plan view of the cylinder liner shown in FIGS. 1
and 2;
[0031] FIG. 4 is a longitudinal sectional view of the scavenging
port portion for illustrating the metal mold casting in one
embodiment of the manufacturing method of cylinder for internal
combustion engine according to the present invention;
[0032] FIG. 5 is a longitudinal sectional view of the suction port
portion for illustrating the metal mold casting in one embodiment
of the manufacturing method of cylinder for internal combustion
engine according to the present invention;
[0033] FIG. 6 is an enlarged partial sectional view showing one
example of the melt intrusion preventing means which is adapted to
be used in one embodiment of the manufacturing method of cylinder
for internal combustion engine according to the present
invention;
[0034] FIG. 7 is a cross-sectional view taken along the line
VII-VII of FIG. 6;
[0035] FIG. 8 is an enlarged partial sectional view showing another
example of the melt intrusion preventing means;
[0036] FIG. 9 is a cross-sectional view taken along the line IX-IX
of FIG. 8;
[0037] FIG. 10 is a longitudinal sectional view of the scavenging
port portion for illustrating the metal mold casting in another
embodiment of the manufacturing method of cylinder for internal
combustion engine according to the present invention;
[0038] FIG. 11 is a longitudinal sectional view of the scavenging
port portion, illustrating the cylinder for a small air-cooled
two-stroke gasoline engine, which can be manufactured according to
one embodiment of the manufacturing method of the cylinder for the
internal combustion engine of the present invention; and
[0039] FIG. 12 is a longitudinal sectional view of the suction port
portion, illustrating the cylinder for a small air-cooled
two-stroke gasoline engine, which can be manufactured according to
one embodiment of the manufacturing method of the cylinder for the
internal combustion engine of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] The present invention will be further explained with
reference to one embodiment of the manufacturing method of a
cylinder for an internal combustion engine where an insert core is
employed according to the present invention.
[0041] The cylinder for an internal combustion engine, which can be
manufactured by the method according to this embodiment, is a
cylinder 1 for a small air-cooled two-stroke gasoline engine as
shown in FIG. 11 (a longitudinal sectional view wherein the
scavenging port thereof is longitudinally sectioned) and FIG. 12 (a
longitudinal sectional view wherein the suction port and exhaust
port thereof are longitudinally sectioned), the engine being
designed to be employed in a portable working machine. This
cylinder 1 is constituted by a main body 2A of the cylinder which
is made of an aluminum alloy and by a cylinder liner 2B, the inner
peripheral surface of which defines a cylinder bore 10. The head
portion 3 of the cylinder is provided with a combustion chamber 4
which is squish dome-shaped for instance. The main body 2A of the
cylinder is provided, on the outer peripheral surface thereof, with
a large number of cooling fins 9 which are formed integral with the
main body 2A. Further, the combustion chamber 4 is provided with an
ignition plug-mounting hole 23 (in which an internal thread 23a
will be formed after cast molding).
[0042] The cylinder 1 is provided with a suction port 11 and with
an exhaust port 12, which are to be closed and opened by the
movement of the piston 60, these suction port 11 and exhaust port
12 being disposed to face each other and off-set level-wise from
each other. The cylinder 1 is also provided with two pairs of
hollow scavenging ducts 14 and 15, each pair being displaced away
from these suction port 11 and exhaust port 12 by an angle of 90
degrees (see also FIG. 3). Namely, the cylinder 1 in this case is a
so-called quaternary fluid scavenging type cylinder where two pairs
of scavenging ports are symmetrically formed with respect to the
longitudinal cross-section F taken along the middle of the exhaust
port 12. The downstream end portion (upper end portion) of each of
the hollow scavenging duct 14 and 15 is constituted by a scavenging
port 16 or 17, thereby providing two pairs of scavenging ports 16
and 17 disposed opposite to each other, which are designed to be
opened and closed by the movement of the piston 60 and are inclined
somewhat upward in the direction opposite to that of the exhaust
port 12 (i.e. directed toward the suction port 11) of the cylinder
bore 10.
[0043] These paired scavenging ducts 14 and 15 are respectively
provided with a half wall. Namely, in order to permit an air-fuel
mixture (which is going to be introduced through each of scavenging
ducts 14 and 15 into each of the scavenging ports 16 and 17 from
the crank chamber (not shown)) to contact with the skirt portion of
the piston 60, paired scavenging inlet openings 21 and 22 are
formed at a lower portion of the scavenging ducts 14 and 15,
respectively, while leaving paired half walls 18 and 19 each having
a predetermined thickness (the thickness of the cylinder liner 2B)
at an upper portion of the scavenging ducts 14 and 15.
[0044] In the manufacture of the cylinder 1 constructed as
described above, the cylinder liner 2B made of an aluminum alloy
pipe having a predetermined wall thickness and a predetermined
inner diameter and provided with two pairs of scavenging ports 16
and 17, two pairs of scavenging inlet openings 21 and 22, the
suction port 11 (the inner end portion 11a thereof), and the
exhaust port 12 (the inner end portion 12a thereof), all of these
openings and ports being formed by a suitable mechanical working;
and the bore-core die 50 as well as two pairs of cores 55 and 56
for scavenging ducts (see FIGS. 4 and 5) all being uncollapsible
and configured so as not to intrude into the each of paired
scavenging ports 16 and 17 as shown in FIGS. 1, 2 and 3 are
prepared in advance.
[0045] The cylinder liner 2B is formed of an aluminum alloy pipe
cut out so as have a predetermined length and an inner diameter
which is slightly smaller than the diameter of the cylinder bore 10
of the finished cylinder 1 (see FIGS. 4 and 5) and provided with
two pairs of scavenging ports 16 and 17, two pairs of scavenging
inlet openings 21 and 22, the suction port 11 (the inner end
portion 11a thereof), and the exhaust port 12 (the inner end
portion 12a thereof), all of these openings and ports being formed
at predetermined locations by means of suitable mechanical working.
Additionally, the cylinder liner 2B is provided near the upper end
thereof with an annular groove 36 in which the main body 2A of the
cylinder is adapted to be fitted.
[0046] The bore-core die 50 is formed of an uncollapsible ordinary
core die which is adapted to be employed in a high pressure die
casting method, and comprises a columnar portion 52 on which the
cylinder liner 2B is externally fitted, a combustion
chamber-forming portion 53 which is formed contiguous with the
upper portion of the columnar portion 52 and configured to
correspond with the combustion chamber 4 of the cylinder 1, and a
proximal end portion 54 which is formed contiguous with the lower
end of the columnar portion 52. This proximal end portion 54 is
connected integrally with the paired scavenging passage-forming
portions 55 (56) corresponding in configuration with the scavenging
ducts 14 and 15, respectively. A lower half portion of the cylinder
liner 2B is designed to be fitted in a gap portion 59 formed
between the columnar portion 52 and the paired scavenging
passage-forming portions 55 and 56.
[0047] In this case, since the bore-core die 50 and the paired
scavenging passage-forming portions 55 and 56 are not intruded into
the scavenging ports 16 and 17 (i.e. under-cut portions), the
bore-core die 50 and the paired scavenging passage-forming portions
55 and 56 are permitted to withdraw downward out of the cylinder 1
after finishing the cast molding.
[0048] As shown in FIGS. 1 and 2, the cylinder liner 2B is set at
first in the bore-core die 50 and the paired scavenging
passage-forming portions 55 and 56, and then, the core 46 for
suction port and the core 47 for exhaust port are set in place as
shown in FIGS. 4 and 5. Thereafter, the metal mold casting is
performed by means of high pressure die casting method.
[0049] In this embodiment, prior to setting the cylinder liner 2B
in the bore-core die 50, melt intrusion prevention means is
provided for preventing melt from entering into the scavenging
ports 16 and 17 on the occasion of metal mold casting. Namely, as
shown in FIGS. 6 and 7, two pairs of blocking members 31 and 32
each having a U-shaped cross-section are detachably mounted in the
scavenging ports 16 and 17, respectively, by introducing them from
the outer peripheral surface side of the cylinder liner 2B. These
blocking members 31 and 32 are respectively made from an aluminum
alloy plate and configured to have the same external size as the
size of the scavenging ports 16 and 17. Further, these blocking
members 31 and 32 are elastically press-contacted with the inner
surface of the scavenging ports 16 and 17, respectively. Further,
these blocking members 31 and 32 are also designed such that a step
portion is not permitted to generate between the scavenging ports
16 and 17 and the scavenging ducts 14 and 15 of the main body 2A of
cylinder.
[0050] Because the outer periphery of each of the scavenging inlet
openings 21 and 22 is in close contact with the scavenging
passage-forming portions 55 and 56, there is no possibility of the
melt entering into the scavenging inlet openings 21 and 22, so that
the melt intrusion prevention means described above is not required
to be provided at these openings. Further, the suction port 11 as
well as the exhaust port 12 are also partially intruded and closed
by the core 46 for suction port (a distal end portion 46a thereof)
and by the core 47 for exhaust port (a distal end portion 47a
thereof), the melt intrusion prevention means is not required to be
provided at these ports. A plug die 51 having a suitable
configuration for forming an ignition plug-mounting hole 28 can be
also provided in the casting.
[0051] As described above, after all of these dies have been set
in, the insert core 30 is set in the cylinder liner 2B and an outer
mold (not shown) is positioned on the outside of the cylinder liner
2B, the die casting is performed by means of the high pressure die
casting to obtain a raw cylinder body 1 as shown in FIGS. 4 and 5.
Thereafter, the bore-core die 50, the scavenging passage-forming
portions 55 and 56, the core 46 for suction port and the core 47
for exhaust port are pulled away, and then, the blocking members 31
and 32 as well as the plug die 51 are removed therefrom.
Subsequently, the inner peripheral surface of the cylinder liner 2B
is subjected to boring and then, the resultant cylinder body is
subjected to predetermined finish treatments such as the formation
of the internal thread portion 23a, thereby obtaining a finished
product of the cylinder 1 as shown in FIGS. 11 and 12.
[0052] According to the method of manufacturing a cylinder for an
internal combustion engine which is constructed as described in
this embodiment, due to the employment of the die and the insert
core both being uncollapsible, it is possible to utilize a
high-pressure die casting method which enables one to obtain a cast
article of high dimensional precision at low cost. Additionally,
since the cylinder liner 2B is provided in advance with the
scavenging ports 16 and 17, the suction port 11 and the exhaust
port 12, it is possible to manufacture the cylinder with higher
precision and at lower cost as compared with the conventional
manufacturing methods such as the method wherein the port portions
such as the scavenging port are cut out by mechanical working after
die casting or the method wherein an insert core to be inserted
into the scavenging port portion is used. At the same time, it is
now possible to obviate the aforementioned problems of the
deterioration of heat conductivity as well as the deformation or
peeling of these port portions due to the remnant of the insert
core in the cast article (cylinder).
[0053] Additionally, since the cylinder liner 2B is formed by
making use of an aluminum alloy pipe, the cylinder liner can be
manufactured at a lower cost as compared with the case where a
liner produced through casting is employed. Further, since the
cylinder liner 2B is formed of the same material (aluminum alloy)
as that of the main body 2A of the cylinder, there is no
possibility of generating any difference in thermal expansion
coefficient as well as in thermal conductivity, thereby making it
possible to inhibit the generation of problems such as peeling
between them, a step portion around the opening such as scavenging
port or misalignment between them. Further, since the cylinder
liner and the main body of the cylinder are formed of the same
material with each other, it is advantageous in terms of recycle
(re-use) of materials.
[0054] Furthermore, since the cylinder liner 2B is provided in
advance with these scavenging port portions 16 and 17, suction port
portion 11 and exhaust port portion 12, there is little possibility
of generating relative misalignment among these port portions, thus
uniquely determining the positions of the scavenging ports 16 and
17, the suction port 11 and the exhaust port 12, thereby making it
possible to provide a cylinder with excellent dimensional precision
and preventing the generation of relative mismatching among the
scavenging ports 16 and 17, the suction port 11 and the exhaust
port 12 with regard to the timing of opening and closing to be
effected by the piston.
[0055] Since the melt intrusion prevention means (blocking members
31, 32 and 35) are provided for preventing melt from entering into
the scavenging ports 16 and 17 on the occasion of metal mold
casting, it is now possible to reliably prevent the melt from
entering into the scavenging ports 16 and 17, thus making it
possible to save the time and labor required for the finish working
of the cylinder such as deflashing work after the casting thereof.
Moreover, since the melt intrusion prevention means is designed so
as to prevent the generation of a step portion between the
scavenging ports 16 and 17 and the scavenging ducts 14 and 15 of
the main body 2A of cylinder, it is possible to prevent the
generation of turbulence in the scavenging gas flow to be injected
in the combustion chamber 4 disposed over the top of piston 60.
[0056] Further, when the inner peripheral edge portion (the inner
peripheral edge portion of the scavenging port 16 is represented by
reference number 16a in FIG. 6) of the opening such as the
scavenging ports 16 and 17, etc. that has been formed in advance in
the cylinder liner 2B is preliminarily chamfered, finish chamfering
work after casting can be easily performed.
[0057] Further, as shown in FIG. 10, when a specific region in the
outer peripheral surface of the cylinder liner 2B, which is
designed to be contacted with the main body 2A of the cylinder is
coated (a covering layer 70 which can be formed through
electroplating, nonelectrolytic plating, ion plating, etc.) with a
metal (for example, zinc, tin, etc.) having a lower melting point
than that of the aluminum alloy, the covering layer 70 thus coated
is enabled to melt on the occasion of casting, resulting in
enhancement of adhesion between the cylinder liner 2B and the main
body 2A of the cylinder. As a result, the heat conduction from the
cylinder liner 2B to the main body 2A of the cylinder can be
enhanced, thus improving the heat dissipation and cooling
properties of the cylinder.
[0058] While in the foregoing one embodiment of the present
invention has been explained in details for the purpose of
illustration, it will be understood that the construction of the
device can be varied without departing from the spirit and scope of
the invention as claimed in the following claims.
[0059] For example, according to the aforementioned embodiment, two
pairs of blocking members 31 and 32 are detachably mounted in the
scavenging ports 16 and 17, respectively, as melt intrusion
prevention means for preventing the melt from entering into the
scavenging ports 16 and 17 on the occasion of metal mold casting.
However, such melt intrusion prevention means may be replaced by
the following structure for example. Namely, as shown in FIGS. 8
and 9, as melt intrusion prevention means, a thick-walled portion
or a rib portion 35 for enabling it to face-contact with each of
the cores 55 and 56 for scavenging duct may be provided around a
peripheral edge portion excluding the lower skirt portion of the
scavenging ports 16 and 17 on the outer peripheral surface of the
cylinder liner 2B in such a manner as to prevent the generation of
a step portion relative to the scavenging ports 16 and 17.
[0060] As would be clear from the foregoing explanation, in the
method of manufacturing a cylinder for an internal combustion
engine according to the present invention, due to the employment of
the die and the insert core both being uncollapsible, it is now
possible to utilize a high-pressure die casting method which
enables to obtain a cast article of high dimensional precision at
low cost. Additionally, since the cylinder liner is provided in
advance with a scavenging port, a suction port and an exhaust port,
it is possible to manufacture the cylinder with higher precision
and at lower cost as compared with the conventional manufacturing
methods such as the method wherein the port portions such as the
scavenging port are cut out by mechanical working after die casting
or the method wherein an insert core to be inserted into the
scavenging port portion is used. At the same time, it is now
possible to obviate the aforementioned problems of the
deterioration of heat conductivity as well as the deformation or
peeling of these port portions due to the remnant of the insert
core in the cast article (cylinder).
[0061] Additionally, since the cylinder liner is formed by making
use of an aluminum alloy pipe, the cylinder liner can be
manufactured at a lower cost as compared with the case where a
liner produced through casting is employed. Further, since the
cylinder liner is formed of the same material (aluminum alloy) as
that of the main body of the cylinder, there is no possibility of
generating any difference in thermal expansion coefficient as well
as in thermal conductivity, thereby making it possible to inhibit
the generation of troubles such as peeling between them, a step
portion around the opening such as scavenging port or misalignment
between them. Further, since the cylinder liner and the main body
of the cylinder are formed of the same material with each other, it
is advantageous in terms of recycle (re-use) of materials.
[0062] Furthermore, since the cylinder liner is provided in advance
with these scavenging port portion, suction port portion and
exhaust port portion, there is little possibility of generating
relative misalignment among these port portions, thus uniquely
determining the positions of the scavenging port, the suction port
and the exhaust port, thereby making it possible to obtain a
cylinder of excellent dimensional precision and preventing the
generation of relative mismatching among the scavenging port, the
suction port and the exhaust port with regard to the timing of
opening and closing to be effected by the piston.
[0063] Since the melt intrusion prevention means is provided for
preventing melt from entering into the scavenging port on the
occasion of metal mold casting, it is now possible to reliably
prevent the melt from entering into the scavenging port, thus
making it possible to save the time and labor required for the
finish working of the cylinder such as deflashing work after the
casting thereof. Moreover, since the melt intrusion prevention
means is designed so as to prevent the generation of a step portion
between the scavenging port and the scavenging duct of the main
body of cylinder, it is possible to prevent the generation of
turbulence in the scavenging gas flow to be injected in the
combustion chamber disposed over the top of piston.
[0064] Further, when the inner peripheral edge portion of the
opening such as the scavenging port etc. that has been formed in
advance in the cylinder liner is preliminarily chamfered, finish
chamfering work after casting can be easily performed.
[0065] Further, when a specific region in the outer peripheral
surface of the cylinder liner, which designed to be contacted with
the main body of the cylinder, is coated (through electroplating,
nonelectrolytic plating, ion plating, etc.) with a metal (for
example, zinc, tin, etc.) having a lower melting point than that of
the aluminum alloy, the metal thus coated is enabled to melt on the
occasion of casting, resulting in enhancement in adhesion between
the cylinder liner and the main body of the cylinder. As a result,
the heat conduction from the cylinder liner to the main body of the
cylinder can be enhanced, thus improving the heat dissipation and
cooling properties of the cylinder.
* * * * *