U.S. patent application number 13/966735 was filed with the patent office on 2013-12-12 for in-cylinder fuel-injection type internal combustion engine, piston for in-cylinder fuel-injection type internal combustion engine and process for manufacturing piston for in-cylinder fuel-injection type internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Kimihiko ANDO, Masashi HARA, Yoshihiko ITO, Kazuhiko ITOH, Mikio KONDOH, Kazuaki NISHINO, Isamu UEDA. Invention is credited to Kimihiko ANDO, Masashi HARA, Yoshihiko ITO, Kazuhiko ITOH, Mikio KONDOH, Kazuaki NISHINO, Isamu UEDA.
Application Number | 20130327491 13/966735 |
Document ID | / |
Family ID | 41200055 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130327491 |
Kind Code |
A1 |
HARA; Masashi ; et
al. |
December 12, 2013 |
IN-CYLINDER FUEL-INJECTION TYPE INTERNAL COMBUSTION ENGINE, PISTON
FOR IN-CYLINDER FUEL-INJECTION TYPE INTERNAL COMBUSTION ENGINE AND
PROCESS FOR MANUFACTURING PISTON FOR IN-CYLINDER FUEL-INJECTION
TYPE INTERNAL COMBUSTION ENGINE
Abstract
A piston for in-cylinder fuel-injection type internal combustion
engine includes a piston body, a low thermal conductor, and a
piston head. The low thermal conductor is disposed on the top of
the piston body. The low thermal conductor includes a low
thermally-conductive substrate, and a coating layer. The low
thermally-conductive substrate has opposite surfaces. The coating
layer includes alumina fine particles (Al.sub.2O.sub.3). The
coating layer is adhered on at least a part one of the opposite
surfaces of the low thermally-conductive substrate that makes a
cast-buried or enveloped surface to be cast buried or enveloped in
the piston head.
Inventors: |
HARA; Masashi; (Nagoya-shi,
JP) ; ITOH; Kazuhiko; (Seto-shi, JP) ; KONDOH;
Mikio; (Toyoake-shi, JP) ; NISHINO; Kazuaki;
(Seto-shi, JP) ; UEDA; Isamu; (Kasugai-shi,
JP) ; ANDO; Kimihiko; (Toyota-shi, JP) ; ITO;
Yoshihiko; (Nagoya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HARA; Masashi
ITOH; Kazuhiko
KONDOH; Mikio
NISHINO; Kazuaki
UEDA; Isamu
ANDO; Kimihiko
ITO; Yoshihiko |
Nagoya-shi
Seto-shi
Toyoake-shi
Seto-shi
Kasugai-shi
Toyota-shi
Nagoya-shi |
|
JP
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
41200055 |
Appl. No.: |
13/966735 |
Filed: |
August 14, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12424808 |
Apr 16, 2009 |
|
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13966735 |
|
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Current U.S.
Class: |
164/75 |
Current CPC
Class: |
F05C 2203/0869 20130101;
F05C 2201/0487 20130101; B22D 19/0027 20130101; F02F 3/0084
20130101; F05C 2201/0412 20130101; F02F 3/26 20130101; B23P 15/10
20130101; F05C 2201/0436 20130101; F02F 3/14 20130101; F05C
2203/0808 20130101; F05C 2201/903 20130101; Y10T 29/49249
20150115 |
Class at
Publication: |
164/75 |
International
Class: |
B22D 19/00 20060101
B22D019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2008 |
JP |
2008-106944 |
Claims
1-10. (canceled)
11. A process for manufacturing piston for in-cylinder
fuel-injection type internal combustion engine, the piston
comprising: a piston body having a top, and being disposed
reciprocably within a cylinder in a cylinder block of the internal
combustion engine; a low thermal conductor for forming a low
thermally-conductive zone whose thermal conductivity is lower than
that of the surroundings, and the low thermal conductor making at
least a part of a fuel collision zone with which liquid fuel is
collidable, the liquid fuel being injected from a fuel injection
valve into the cylinder, the fuel injection valve being disposed in
a cylinder head that is disposed on the cylinder block; and a
piston head in which the low thermal conductor being disposed on
the top of the piston body is cast buried; the manufacturing
process comprising the steps of: adhering a coating material
comprising alumina fine particles onto at least a part of one of
opposite surfaces of a low thermally-conductive substrate, thereby
forming a coating layer on one of the opposite surfaces; and
casting the piston head while contacting the one of the opposite
surfaces of the low thermally-conductive substrate that is provided
with the coating layer with a molten metal of aluminum alloy,
thereby making an aluminum-alloy piston head in which the low
thermal conductor is cast buried.
12. The manufacturing process according to claim 11, wherein the
adhering step comprises a step of immersing at least a part of one
of the opposite surfaces of the low thermally-conductive substrate
into a dispersion liquid in which the coating material is dispersed
in a dispersant.
13. The manufacturing process according to claim 11, wherein the
adhering step comprises a step of applying a dispersion liquid in
which the coating material is dispersed in a dispersant onto at
least a part of one of the opposite surfaces of the low
thermally-conductive substrate.
14. The manufacturing process according to claim 12, wherein the
adhering step further comprises a step of drying the low
thermally-conductive substrate which has been immersed into the
dispersion liquid.
15. The manufacturing process according to claim 13, wherein the
adhering step further comprises a step of drying the low
thermally-conductive substrate on which the dispersion liquid has
been applied.
16. The manufacturing process according to claim 12, wherein the
dispersant comprises water or alcohol.
17. The manufacturing process according to claim 13, wherein the
dispersant comprises water or alcohol.
18. The manufacturing process according to claim 12, wherein
dispersion liquid comprises the coating material in a mixing
proportion of from 1 to 2 by mass with respect to a mass of the
dispersant.
19. The manufacturing process according to claim 13, wherein
dispersion liquid comprises the coating material in a mixing
proportion of from 1 to 2 by mass with respect to a mass of the
dispersant.
20. The manufacturing process according to claim 11, wherein the
coating material comprises at least one member that is selected
from the group consisting of alumina powders and alumina-containing
clays.
21. The manufacturing process according to claim 20, wherein the
coating material comprises a mixture of an alumina powder and an
alumina-containing clay.
22. The manufacturing process according to claim 20, wherein the
alumina-containing clay is mixed with the alumina powder in a
mixing proportion of from 0 to 80 by mass with respect to a mass of
the alumina powder.
23. The manufacturing process according to claim 20, wherein the
alumina-containing clays comprise an alumina-silica hydrate.
24. The manufacturing process according to claim 14, wherein the
low thermally-conductive substrate is dried at a temperature of
50.degree. C. or more in the drying step.
25. The manufacturing process according to claim 15, wherein the
low thermally-conductive substrate is dried at a temperature of
50.degree. C. or more in the drying step.
Description
INCORPORATION BY REFERENCE
[0001] The present invention is based on Japanese Patent
Application No. 2008-106,944, filed on Apr. 16, 2008, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an in-cylinder
fuel-injection type internal combustion engine, such as diesel
engines and gasoline engines, a piston for in-cylinder
fuel-injection type internal combustion engine, piston which is
provided with a low thermal conductor for facilitating the
atomization or vaporization of liquid fuel that is injected into
the internal combustion engine's cylinder, and a process for
manufacturing the piston.
[0004] 2. Description of the Related Art
[0005] As environmental consciousness has been growing, it has been
required strongly to make internal combustion engines, such as
diesel engines and gasoline engines that are used for automobiles,
motorcycles and industrial machines, consume fuels less, and to
make the exhaust gases being emitted from them clean. For example,
from the viewpoint of saving fuel consumption, in-cylinder
fuel-injection type gasoline engines have come to be adopted even
in ordinary commercially-available cars recently.
[0006] However, in in-cylinder fuel-injection type internal
combustion engine, it is not easy to always atomize or vaporize the
fuel fully, because the injection amount and injection timing of
fuel that is injected into the cylinders fluctuate depending on
loads to the internal combustion engine. Accordingly, an adverse
effect, such as the incomplete combustion of fuel, has arisen,
albeit only slightly, so that the fuel consumption might have
degraded or the emissions of hydrocarbons and soot might have
increased in the exhaust gases, though even temporarily, when cold
running the internal combustion engine. Although recent automobiles
have certainly been equipped with exhaust-gas purifying catalytic
apparatuses, the catalysts are not activated unless their
temperatures are raised to a certain extent. Consequently, it has
been likely that such an instance that the exhaust gases are
purified insufficiently might occur when cold running the internal
combustion engines, that is, immediately after starting them up,
for instance.
[0007] In particular, in-cylinder fuel-injection type gasoline
engine carries out the stratified charge combustion in super
fuel-lean atmosphere with high air-fuel ratio in addition to
carrying out uniformly-mixed combustion. Accordingly, if the fuel
is atomized or vaporized insufficiently around the spark plugs when
the internal combustion engine carries out the stratified charge
combustion, unburned gases might be discharged, for instance, as
the ignitability of fuel degrades. Consequently, it might be even
possible for such insufficient atomization or vaporization to
adversely affect making the internal combustion engine consume fuel
less and making the exhaust gases clean.
[0008] Under such circumstances, in order to facilitate the
atomization or vaporization of injected fuel, it has been proposed
heretofore, for instance, to provide the top surface of piston with
a low thermally-conductive zone, which can become a higher
temperature than that of the surroundings, within the fuel
collision zone. For example, Japanese Unexamined Patent Publication
(KOKAI) Gazette No. 2000-186,617 (i.e., Japanese Patent Gazette No.
3,551,801) discloses such a technique specifically.
[0009] Japanese Patent Gazette No. 3,551,801 proposes to place a
plate that comprises a low thermally-conductive material (that is,
a low thermal conductor) on the fuel collision part in the top
surface of a piston for in-cylinder fuel-injection type
spark-ignition engine in order to facilitate the evaporation of
fuel and in order to decrease the adhesion of fuel. Besides placing
the plate, Japanese Patent Gazette No. 3,551,801 also proposes to
form a highly heat-insultative minute-intersticed layer between the
plate and the piston body by turning the rear surface of the plate
into an irregular shape.
[0010] However, according to surveys and studies that the present
inventors have carried out so far, it has been found difficult to
actually form such a minute-intersticed layer as disclosed in
Japanese Patent Gazette No. 3,551,801 when the plate whose rear
surface is turned into an irregular shape is simply cast buried or
enveloped in the piston with an aluminum-alloy molten metal. That
is, the formation of the minute-intersticed layer is hardly
possible because the molten metal flows unstably during the cast
burying or enveloping. Moreover, turning the rear surface of the
plate as an irregular shape is likely to result in increased
manufacturing costs. In addition, considering the large explosive
forces that act onto the piston, it is impossible to thin out the
plate on the rear-surface side or reduce the plate's thickness from
the viewpoint of the strength and rigidity.
[0011] The present invention has been developed in view of such
circumstances. Specifically, it is an object of the present
invention to provide a piston for in-cylinder fuel-injection type
internal combustion engine, piston which enables a low thermal
conductor that is cast buried or enveloped in the piston's top to
exhibit furthermore enhanced heat insulating property more securely
and actively. Moreover, it is another object of the present
invention to provide an in-cylinder fuel-injection type internal
combustion engine using the piston. In addition, it is still
another object of the present invention to provide a process for
manufacturing the piston for in-cylinder fuel-injection type
internal combustion engine.
SUMMARY OF THE INVENTION
[0012] The present inventors studied earnestly to solve the
aforementioned problems. As a result of their repeated trial and
error, they arrived at thinking of disposing a coating layer, which
comprises alumina fine particles (Al.sub.2O.sub.3), on the rear
surface of a low thermally-conductive substrate that is cast buried
or enveloped in the top of piston. Moreover, they newly found out
that, when cast burying or enveloping the low thermally-conductive
substrate with the coating layer being provided in the top of
piston using an aluminum-alloy molten metal, it is possible to form
a minute-intersticed layer in which the alumina fine particles
intervene between a cast-buried or enveloped surface, namely, the
rear surface of the substrate, and the body of the resulting
piston. Thus, based on such an achievement, they arrived at
completing the present invention as described below.
Piston for In-cylinder Fuel-injection Type Internal Combustion
Engine
[0013] For example, a piston for in-cylinder fuel-injection type
internal combustion engine according to the present invention
comprises:
[0014] a piston body having a top, and being disposed reciprocably
within a cylinder in a cylinder block of the internal combustion
engine;
[0015] a low thermal conductor for forming a low
thermally-conductive zone whose thermal conductivity is lower than
that of the surroundings, and the low thermal conductor making at
least a part of a fuel collision zone with which liquid fuel is
collidable, the liquid fuel being injected from a fuel injection
valve into the cylinder, the fuel injection valve being disposed in
a cylinder head that is disposed on the cylinder block; and
[0016] a piston head in which the low thermal conductor being
disposed on the top of the piston body is cast buried;
[0017] the piston head comprising an aluminum-alloy casting;
and
[0018] the low thermal conductor comprising a low
thermally-conductive substrate having opposite surfaces, and a
coating layer being adhered on at least a part of one of the
opposite surfaces of the low thermally-conductive substrate that
makes a cast-buried surface to be cast buried in the top of the
piston body, and the coating layer comprising alumina
(Al.sub.2O.sub.3) fine particles.
[0019] The piston for in-cylinder fuel-injection type internal
combustion engine according to the present invention makes it
possible to reliably form the low thermal-conductive zone, which
exhibits very low thermally-conducting property, in the fuel
collision zone. Consequently, the present piston enables liquid
fuels, which are injected in the cylinder of the internal
combustion engine, to atomize or vaporize more reliably. Thus, an
in-cylinder fuel-injection type internal combustion engine using
the present piston makes it possible to upgrade the fuel
consumption and purify the exhaust gases more reliably than
conventional ones do.
[0020] Meanwhile, it has not necessarily been cleared yet in detail
how the piston for in-cylinder fuel-injection type combustion
engine according to present invention operates to produce the
outstanding advantages as described above. However, it is believed
tentatively to be as hereinafter described.
[0021] First off, the alumina fine particles are so-called ceramic
fine particles, and they themselves exhibit lower thermal
conductivity than aluminum alloys and iron alloys do. Accordingly,
the coating layer itself that comprises the alumina fine particles
turns into a so-called heat insulating layer. Consequently, the
coating layer inhibits heat from transferring between the low
thermal conductor proper and the piston body, namely, the
cast-product part that is made of aluminum alloy. Therefore, the
low thermal conductor becomes likely to undergo temperature
rise.
[0022] Moreover, in the piston for in-cylinder fuel-injection type
combustion engine according to the present invention, the presence
of the coating layer makes it easy to form a minute-intersticed
layer between the low thermal conductor per se and the piston body
in addition to the coating layer's own low thermally-conducting
property. Although it is difficult to identify the form of the
minute interstices, it does not matter whether the minute
interstices can be either continuous minute interstices in the
coating layer or scattering minute independent pores that exist
between the alumina fine particles therein, for instance. In any
case, the minute-intersticed layer demonstrates good heat
insulating property because it exhibits remarkably lower thermal
conductivity than that of the low thermally-conductive substrate
proper.
[0023] Therefore, it eventually becomes possible to obstruct the
heat transfer from the low thermal conductor to the piston body
more greatly and reliably than having been done conventionally,
because the heat insulating property resulting from the
minute-intersticed layer are added to the heat insulating property
of the low thermally-conductive substrate itself and the heat
insulating property of the coating layer itself. As a result, the
low thermal conductor with which liquid fuels collide can
facilitate the atomization or vaporization of the liquid fuels,
because the low thermal conductor is likely to become higher
temperatures than that of the surroundings far better than
conventional ones do, and more reliably as well. All in all, the
low thermal conductor makes it possible to upgrade the fuel
consumption of in-cylinder fuel-injection type internal combustion
engine and the performance for purifying the exhaust gases emitted
from the same.
[0024] In addition to the above, the piston for in-cylinder
fuel-injection type combustion engine according to the present
invention comprises the low thermal conductor that can be made
virtually by simply providing one of the opposite surfaces to be
cast buried or enveloped with the coating layer. Accordingly, the
present piston does not require such processes at all that result
in increasing the manufacturing costs. Consequently, the present
piston enables manufacturers to intend reducing the manufacturing
costs.
[0025] Note herein that it has not necessarily been possible yet to
detail what a mechanism works to form the minute-intersticed layer
at around the boundary surface between the low thermal conductor
and the piston body when the low thermal conductor with the coating
layer being provided is cast buried or enveloped in the piston
body. However, it is believed to be as described below at present.
That is, the coating layer that comprises the alumina fine
particles is less likely to be wetted with an aluminum-alloy molten
metal. Because of the coating layer's this low wettability, the
aluminum-alloy molten metal has been repelled at sections where it
comes in contact with the coating layer. Accordingly, the minute
interstices between the alumina fine particles are hardly
impregnated with the aluminum-alloy molten metal. Consequently, it
seems that the low thermal conductor and the piston body are not
joined to each other so that the minute interstices come to be
formed at the boundary-surface sections between them.
[0026] Moreover, it appears at first glance that such minute
interstices or the minute-intersticed layer might become the cause
of the deformation or flexure of the low thermal conductor onto
which the great explosive forces act. However, the deformation or
flexure of the low thermal conductor, which might result from the
minute interstices or minute-intersticed layer, does not matter,
because the minute interstices or minute-intersticed layer that is
formed actually is an assemblage of fine pores whose pore diameters
are from 5 to 50 .mu.m approximately, or because the resulting
minute interstices or minute-intersticed layer comprises only voids
whose thicknesses are no larger than 0.5 mm approximately. Besides
that, the resultant minute interstices or minute-intersticed layer
does not make absolutely perfect minute interstices. That is, the
alumina fine particles that constitute the coating layer are
present in such a state that they intervene between the low thermal
conductor and the piston body. This can be approximated to such a
state that a large number of the alumina fine particles turn into
so-called "pillars" to support the minute interstices. In addition
to that, the alumina fine particles are ceramic particles with high
strength. Therefore, it is believed that the deformation or flexure
of the low thermal conductor, which might result from the minute
interstices or minute-intersticed layer, does not matter even when
the low thermal conductor is subjected to the great explosive
forces repeatedly.
Process for Manufacturing Piston for In-cylinder Fuel-Injection
Type Internal Combustion Engine
[0027] It is possible to grasp the present invention as a process
for manufacturing the above-described piston for in-cylinder
fuel-injection type internal combustion engine as well. For
example, it is allowable to comprehend the present invention as a
process for manufacturing piston for in-cylinder fuel-injection
type internal combustion engine, the piston comprising: a piston
body having a top, and being disposed reciprocably within a
cylinder in a cylinder block of the internal combustion engine; a
low thermal conductor for forming a low thermally-conductive zone
whose thermal conductivity is lower than that of the surroundings,
and the low thermal conductor making at least a part of a fuel
collision zone with which liquid fuel is collidable, the liquid
fuel being injected from a fuel injection valve into the cylinder,
the fuel injection valve being disposed in a cylinder head that is
disposed on the cylinder block; and a piston head in which the low
thermal conductor being disposed on the top of the piston body is
cast buried;
[0028] the manufacturing process comprises the steps of:
[0029] adhering a coating material comprising alumina fine
particles onto at least a part of one of opposite surfaces of a low
thermally-conductive substrate, thereby forming a coating layer on
one of the opposite surfaces; and
[0030] casting the piston head while contacting the one of the
opposite surfaces of the low thermally-conductive substrate that is
provided with the coating layer with a molten metal of aluminum
alloy, thereby making an aluminum-alloy piston head in which the
low thermal conductor is cast buried.
In-cylinder Fuel-Injection Type Internal Combustion Engine
[0031] Moreover, it is possible to grasp the present invention not
only as the present piston per se for in-cylinder fuel-injection
type internal combustion engine but also as an in-cylinder
fuel-injection type internal combustion chamber proper using the
same. For example, it is allowable to comprehend the present
invention as an in-cylinder fuel-injection type internal combustion
engine, which comprises:
[0032] a cylinder block having a cylinder;
[0033] a cylinder head being disposed on the cylinder block;
[0034] a fuel injection valve being disposed in the cylinder head;
and
[0035] the above-described piston for in-cylinder fuel-injection
type internal combustion engine according to the present
invention.
Optional Constructions
[0036] In addition to the above-described fundamental
constructions, it is proper that the present invention can further
comprise any one optional feature that is selected from the
following optional constructions given below, or any two or more of
optional features that are selected therefrom. It should be noted
however that it is feasible to apply the optional constructions
that are selected from those described below at discretion and in
superposed or composite manners to the piston, in-cylinder
fuel-injection type internal combustion engine and manufacturing
process according to the present invention.
[0037] Moreover, the piston, in-cylinder fuel-injection type
combustion engine using the same, and process for manufacturing the
same according to the present invention will be hereinafter
described separately or distinctively for convenience. However, it
is feasible to appropriately combine any two or more of the
following optional constructions with each other at will beyond the
categories. That is, it is needless to say that the optional
construction that is directed to a coating material for the low
thermal conductor, for instance, can be relevant not only to the
present piston per se for in-cylinder fuel-injection type internal
combustion engine, but also to the present process for
manufacturing the same. In addition, although it simply appears
that an optional construction is directed to a "process," the
optional construction can turn into an optional construction that
is directed to a "product" when comprehending it as a claim being
written in the form of "product-by-process."
(I) Optional Constructions Relevant to Piston for In-Cylinder
Fuel-Injection Type Internal Combustion Engine
[0038] The following are optional constructions for the piston
according to the present invention:
[0039] (I)-(i) The low thermally-conductive substrate can
preferably comprise: manganese (Mn) in an amount of from 5 to 35%
by mass; carbon (C) in an amount of from 0.5 to 1.5% by mass, and
the balance of iron (Fe) and inevitable impurities or modifying
elements; when the entirety is taken as 100% by mass. For example,
the modifying elements can preferably be Si, P, S, O, N, Cu, Ni,
Cr, Mo, Nb, V, and Ti Moreover, the Mn content can more preferably
be from 7 to 30% by mass; and the C content can more preferably be
from 0.8 to 1.2% mass;
[0040] (I)-(ii) The low thermally-conductive substrate can
preferably have the cast-buried or cast-enveloped surface that is
formed as an irregular shape partially at least;
[0041] (I)-(iii) The alumina fine particles can preferably exhibit
an average particle diameter of from 5 to 50 g m. Moreover, the
average particle diameter can more preferably be from 10 to 40
.mu.m;
[0042] (I)-(iv) The coating layer can preferably have a thickness
of from 0.01 to 0.30 mm. Moreover, the thickness can more
preferably be from 0.10 to 0.20 mm;
[0043] (I)-(v) The alumina fine particles can preferably be present
in the coating layer in a proportion of from 5 to 100% by volume
when the entire coating layer is taken as 100% by volume. Moreover,
the presence proportion can more preferably be from 20 to 80% by
volume; and
[0044] (I)-(vi) The low thermally-conductive substrate can
preferably comprise a Ti alloy or a stainless alloy (or Fe--Cr
alloy).
(II) Optional Constructions Relevant to Process for Manufacturing
Piston for In-Cylinder Fuel-Injection Type Internal Combustion
Engine
[0045] Optional constructions for the process for manufacturing
piston for in-cylinder fuel-injection type internal combustion
engine according to the present invention are as follows:
[0046] (II)-(i) The adhering step can preferably comprise a step of
immersing at least a part of one of the opposite surfaces of the
low thermally-conductive substrate into a coating solution or
dispersion liquid in which the coating material is dispersed in a
solvent or dispersant;
[0047] (II)-(ii) The adhering step can preferably comprise a step
of applying a coating solution or dispersion liquid in which the
coating material is dispersed in a solvent or dispersant onto at
least a part of one of the opposite surfaces of the low
thermally-conductive substrate;
[0048] (II)-(iii) The adhering step can preferably further comprise
a step of drying the low thermally-conductive substrate, which has
been immersed into the coating solution or dispersion liquid, or on
which the coating solution or dispersion liquid has been
applied;
[0049] (II)-(iv) The solvent or dispersant can preferably comprise
water or alcohol;
[0050] (II)-(v) In preparing the coating solution or dispersion
liquid, the coating material can preferably be mixed with the
solvent or dispersant in a proportion of from 1 to 2 by mass with
respect to a mass of the solvent or dispersant;
[0051] (II)-(vi) The coating material can preferably comprise at
least one member that is selected from the group consisting of
alumina powders and alumina-containing clays;
[0052] (II)-(vii) The coating material can preferably comprise a
mixture of an alumina powder and an alumina-containing clay;
[0053] (II)-(viii) In preparing the mixture, the alumina-containing
clay can preferably be mixed with the alumina powder in a
proportion of from 0 to 80 by mass with respect to a mass of the
alumina powder;
[0054] (II)-(ix) The alumina-containing clays can preferably
comprise an alumina-silica hydrate; and
[0055] (II)-(x) The low thermally-conductive substrate can
preferably be dried at a temperature of 50.degree. C. or more in
the drying step.
(III) Optional Constructions Relevant to In-Cylinder Fuel-Injection
Type Internal Combustion Engine
[0056] The in-cylinder fuel-injection type internal combustion
engine according to the present invention can naturally make not
only gasoline engines but also diesel engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] A more complete appreciation of the present invention and
many of its advantages will be readily obtained as the same becomes
better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings and detailed specification, all of which forms a part of
the disclosure.
[0058] FIG. 1 is a partial cross-sectional diagram for illustrating
an in-cylinder fuel-injection type internal combustion engine
according to an example of the present invention.
[0059] FIG. 2 is a photograph for showing a vertical
cross-sectional view of a test specimen in which a low thermal
conductor that is directed to a piston according to another example
of the present invention is cast buried or enveloped.
[0060] FIG. 3 is a photograph for showing a vertical
cross-sectional view of a comparative test specimen in which
another low thermal conductor that is not provided with any coating
layer is cast buried or enveloped.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] Having generally described the present invention, a further
understanding can be obtained by reference to the specific
preferred embodiments which are provided herein for the purpose of
illustration only and not intended to limit the scope of the
appended claims.
[0062] The present invention will be described in more detail while
naming specific embodiment modes. It should be noted that,
including the following embodiment modes, disclosures being
described in the present specification are appropriately applicable
not only to an in-cylinder fuel-injection type internal combustion
engine according to the present invention and a piston for the same
but also to a process for manufacturing the piston. Moreover, it
should be also noted that which of the following embodiment modes
is considered best depends on objects to which they are applied and
on the objects' performance requirements.
(A) Low Thermally-Conductive Substrate
[0063] It is allowable that a low thermally-conductive substrate
that is directed to the present invention can comprise
stainless-alloy system materials and Ti-alloy system materials, in
addition to Fe--Mn--C-alloy system materials. The low
thermally-conductive substrate can preferably comprise a material
whose thermal conductivity is lower than that of an aluminum alloy
making a piston according to the present invention. However, in the
low thermally-conductive substrate, it does not necessarily matter
to what extent the low thermal-conductive substrate exhibits low
thermal conductivity specifically, because a later-described
coating layer produces great heat-insulating effect.
[0064] Since the low thermally-conductive substrate is cast buried
or enveloped in a piston according to the present invention which
reciprocates at high speeds and at the same to which the large
explosive forces act, the low thermally-conductive substrate does
not disturb the piston's functions. Concretely speaking, it is
necessary that the low thermally-conductive substrate can be
provided with required mechanical strength and rigidity, and at the
same time with such thermal fatigue strength that it can withstand
repeated cooling/heating cycles, for instance. In particular, from
the viewpoint of the latter, the low thermally-conductive substrate
can preferably exhibit a coefficient of linear expansion that can
be approximated to the coefficient of linear expansion of aluminum
alloy, a major material for making a piston according to the
present invention. Moreover, the low thermally-conductive substrate
can preferably exhibit such castability (or cast-burying or
enveloping ability) that it exerts good adhesiveness to the
aluminum alloy, excepting a surface to which a later-described
coating layer adheres.
[0065] When the low thermally-conductive substrate comprises an
Fe--Mn--C-alloy system material, it can include one or more
modifying elements in a small amount, in addition to Mn, C and Fe
and inevitable impurities that make the balance. The "modifying
elements" are elements that the low thermally-conductive substrate
is allowed to contain auxiliarily or secondarily as far as they do
not impair the characteristics of the low thermally-conductive
substrate fundamentally. It does not matter whether the modifying
elements improve the characteristic of the low thermally-conductive
substrate or not. Even if they do not produce such an effect of
improving the characteristics, they are included in the category of
modifying elements as far as they are elements that do not impair
the fundamental characteristics of the low thermally-conductive
substrate. Moreover, the "inevitable impurities" include impurities
that are contained in raw materials, and impurities that get mixed
in during the production, that is, they are elements that are
difficult to remove for cost or technical reasons.
[0066] For example, an Fe--Mn--C alloy that the present inventors
have been developing separately will be hereinafter described
supplementarily.
[0067] Firstly, when the Fe--Mn--C alloy comprises Mn in an amount
of from 5 to 35% by mass with respect to the entirely taken as 100%
by mass, the resulting low thermally-conductive substrate can
exhibit desirable thermal conductivity and linear-expansion
coefficient stably. On the other hand, when it comprises Mn too
less, it is not preferable because the resultant low
thermally-conductive substrate has exhibited sharply increasing
thermal conductivity. Moreover, when it comprises Mn too much, the
resulting low thermally-conductive substrate does not exhibit a
desirable linear-expansion coefficient because the linear-expansion
coefficient has declined. A preferable Mn content of the Fe--Mn--C
alloy can be from 7 to 30% by mass with respect to the entirely
taken as 100% by mass.
[0068] Secondly, it is possible for the Fe--Mn--C alloy, which
comprises C in an amount of from 0.5 to 1.5% by mass with respect
to the entirely taken as 100% by mass, to produce the low
thermally-conductive substrate that exhibits desirable thermal
conductivity and linear-expansion coefficient stably. On the
contrary, the Fe--Mn--C alloy, which comprises C too less, is not
preferable because it has resulted in making the low
thermally-conductive substrate that exhibits thermal conductivity
which increases sharply and linear-expansion coefficient which is
lower than the lower limit of the desirable range. On the other
hand, the Fe--Mn--C alloy, which comprises an increased amount of
C, is preferable because it can produce the low
thermally-conductive substrate whose thermal conductivity and
linear-expansion coefficient approach so as to fall in their
desirable ranges. However, the Fe--Mn--C alloy, which comprises C
too much, is not preferable because it has resulted in making the
low thermally-conductive substrate with sharply decreasing tensile
strength to such an extent that it might serve no practical use.
The Fe--Mn--C alloy can preferably comprise C in an amount of from
0.8 to 1.2% by mass with respect to the entirety taken as 100% by
mass.
[0069] Thirdly, Fe is the major component that makes the Fe--Mn--C
alloy. However, when Mn and C are added to Fein the aforementioned
specific amounts, the resulting Fe--Mn--C alloy comes to exhibit
characteristics that are much distinct from those of usual iron
system materials. Observing the Fe--Mn--C alloy from the viewpoint
of thermal conductivity and linear-expansion coefficient at least,
the Fe--Mn--C alloy demonstrates the above-described good
characteristics so that it cannot be considered an iron-based
alloy.
[0070] Fourthly, the basic constituent elements of the Fe--Mn--C
alloy are the three elements, namely, Mn, C and Fe. However, in
addition to Mn, C and Fe, the Fe--Mn--C alloy can further comprise
a modifying element. As the modifying element, it is possible to
name Si, P, S, O, N, Cu, Ni, Cr, Mo, Nb, V and Ti, for instance.
The content of such a modifying element can usually be a trace
amount of from 0.01 to 1% by mass with respect to the entirety
taken as 100% by mass.
[0071] Note that the numeric ranges, such as "from `x` to `y`" as
set forth in the present specification, include the lower limit
value, "x," and the upper limit value, "y," unless otherwise
specified. Moreover, it should be noted that, in addition to the
numeric values that are specified as the upper limit values and
lower limit values as described in the present specification, it is
possible to optionally combine any of the following numeric values,
such as those being recited in the section of "EXAMPLE," to
establish new upper and lower limit values or new numeric ranges
like "from `a` to `b`"
[0072] Finally, the Fe--Mn--C alloy exhibits thermal conductivity
that is smaller than that of aluminum alloy, a material for making
piston, by a factor of from 1/10 to 1/20, for example, from 7 to 13
W/mK. On the other hand, the coefficient of linear expansion of the
Fe--Mn--C alloy is about 20.times.10.sup.-6/K (for example, from 15
to 25.times.10.sup.-6/K), and can be approximated to that of the
piston body virtually. Therefore, even when the low thermal
conductor whose composition differs from that of the fuel collision
zone in the piton's top, it is less likely to cause the
inconveniences, such as the coming off or breakdown between the low
thermal conductor and the piston head, and the thermal-fatigue
breakdown that results from being subjected to repetitive thermal
stresses.
[0073] Moreover, it is possible to modify only the superficial
layer of the low thermally-conductive alloy that is directed to the
present invention, namely, the outermost layer of the low-thermally
conductive substrate alone, if necessary, by carrying out a known
carburizing treatment or nitriding treatment, independently of a
later-described coating treatment that is directed to the present
invention. The purpose of this additional treatment is not limited
to improving the low thermally-conductive alloy's strength. That
is, it is feasible to utilize the additional treatment for the
undercoating treatment for diamond-like-carbon (or DLC) film, for
instance. In addition, when the low thermally-conductive substrate
comprises a sintered body, it is allowable to subject one of the
surfaces of the low thermally-conductive substrate to a
pore-closing treatment. The pore-closing treatment inhibits the
inside of the low thermally-conductive substrate from being
impregnated with liquid fuel, and thereby prevents the liquid fuel
from vaporizing insufficiently.
[0074] It is possible to appropriately demarcate or form the low
thermally-conductive substrate as such a configuration that
coincides with the piston head's configuration or the fuel
collision zone's configuration. Moreover, the low
thermally-conductive substrate can comprise either a sintered body
or a cast body. However, the low thermally-conductive substrate
comprising a sintered body makes it possible to reduce processing
costs by means of net shaping, and to increase or decrease the
thermal conductivity by means of controlling the porosity (or
density).
[0075] Moreover, it is allowable that one of the opposite surfaces
of the low thermally-conductive substrate can be provided with a
minute irregular surface. Such a minute irregular surface enlarges
the low thermally-conductive substrate's superficial area, thereby
facilitating the vaporization of liquid fuel that makes contact
with the low thermally-conductive substrate. In addition, it is
allowable to turn one of the opposite surfaces of the low
thermally-conductive substrate that is to be case buried or
enveloped into an irregular surface in order to form, besides the
minute interstices with sizes that the coating layer makes, the
other second minute interstices that are larger than the first
minute interstices with such sizes.
(B) Coating Treatment
(B)-1 Coating Material
[0076] A coating material comprises alumina fine particles. The
coating material is adhered onto one of the opposite surfaces of
the low thermally-conductive substrate to form a coating layer.
[0077] Note that the process for producing the alumina fine
particles, a major component of the coating material, and the
average particle diameter and existence form of the alumina fine
particles do not matter at all. However, in order to give the
coating layer a desirable form, it is possible to optionally select
the raw materials or composition of the coating material and the
average particle diameter of the alumina fine particles. For
example, it is allowable to choose the alumina fine particles whose
average particle diameter is from 5 to 50 .mu.m, preferably from 10
to 40 .mu.m.
[0078] As for the coating material, although it is allowable to use
an alumina powder that includes only the alumina fine particles
genuinely or 100%, it is possible as well to use a mixture powder
that includes the other ceramic fine particles, such as silica fine
particles, in addition to the alumina fine particles. Moreover, as
for the coating material, it is also possible to use an
alumina-containing clay that contains alumina. In addition, it is
allowable as well to use a mixture of the alumina powder and a clay
that contains alumina. For example, it is preferable to mix an
alumina-containing clay with the alumina powder in a proportion of
from 0 to 80 by mass with respect to a mass of the alumina powder
(i.e., alumina-containing clay/alumina power).
[0079] For reference, the alumina-containing clay can be an
alumina-silica hydrate, namely, an adulterant of alumina, silica
and water, for instance. That is, the alumina-containing clay can
comprise Al.sub.2O.sub.3.2SiO.sub.2.2H.sub.2O or
Al.sub.2O.sub.3.2SiO.sub.2.4H.sub.2O, Note that, in addition to the
aforementioned powders and clays, the coating material can further
include, for example, a binder that is required so as to make the
alumina fine particles adhere onto the low thermally-conductive
substrate.
(B)-2 Adhering Step
[0080] The adhering step is for adhering the coating material onto
the low thermally-conductive substrate. Although it does not matter
whatever specific method of adhering the coating material is
employed, the following are available, for instance: an immersion
method of immersing the low thermally-conductive substrate into a
coating solution or dispersion liquid in which the coating material
is dissolved or dispersed in a solvent or dispersant; and an
application method of applying such a coating solution or
dispersion liquid onto the low thermally-conductive substrate.
Moreover, it is possible to carry out the application method by
means of coating the coating solution or dispersion liquid with a
brush, or by means of spraying the coating solution or dispersion
liquid with a spray gun.
[0081] As for the solvent or dispersant that is used for preparing
the coating solution or dispersion liquid, it is possible to use
organic solvents, such as alcohols, in addition to water. The water
is not only inexpensive but also puts load less onto environments.
On the other hand, alcohols with low boiling point upgrade the
present manufacturing process's productivity, because they dry
quickly.
[0082] It is allowable to control a mixing proportion of the
coating material with the solvent or dispersant in such a range
that makes it possible to carry out the adhering step and the
subsequent drying step efficiently. For example, it is preferable
that the mixing proportion (coating material/solvent or dispersant)
can fall in a range of from 1 to 2 by mass, more preferably from
1.2 to 1.8 by mass.
(B)-3 Drying Step
[0083] The drying step is for drying the coating solution or
dispersion liquid that is adhered on one of the opposite surfaces
of the low thermally-conductive substrate. The drying step helps
forming the coating layer, which is made mainly of the alumina fine
particles, on one of the opposite surfaces of the low
thermally-conductive substrate fully.
[0084] It is difficult to specify the temperature and time for
drying the coating solution or dispersion liquid in general,
because they depend on the composition and adhered amount of the
coating solution or dispersion liquid. However, according to the
present inventors' investigations or studies, drying the coating
solution or dispersion liquid at a high temperature relatively for
a short period of time comparatively makes it likely to inhibit
drawbacks or inconveniences, such as swellings other than the
desirable minute interstices, from occurring in the resulting
coating layer.
[0085] For example, at the drying step, it is allowable to dry the
coating solution or dispersion liquid at about a temperature of
from 300 to 600.degree. C. for a time period of from 20 to 60
minutes approximately. Note that a preferable drying temperature
can be from 400 to 550.degree. C. Moreover, as for an atmosphere
for drying the coating solution or dispersion liquid, it is
allowable to dry the low thermally-conductive substrate with the
coating solution or dispersion liquid being adhered in an air
atmosphere or in an inert atmosphere as far as it provides
environment that enables evaporated components of the coating
solution or dispersion liquid to be discharged.
Example
[0086] Hereinafter, the present invention will be described in more
detail with reference to a specific example.
In-cylinder Fuel-Injection Type Internal Combustion Engine
[0087] FIG. 1 illustrates an in-cylinder fuel-injection type spark
ignition engine 1 (hereinafter simply referred to as "engine 1"),
an example that is directed to an in-cylinder fuel-injection type
internal combustion engine according to present invention.
[0088] The engine 1 comprises a cylinder block 30, a cylinder head
40, and a piston 10. The cylinder head 40 is fixed on the cylinder
block 30 by way of a not-shown gasket with not-shown head bolts.
The piston 10 is fitted into a cylinder 31 of the cylinder block 30
reciprocably.
[0089] The cylinder block 30, the cylinder head 40, and the piston
10 are made of aluminum alloy. For example, the piston 10 is made
of AC8A alloy (as per JIS), an aluminum alloy whose thermal
conductivity is 134 W/mK at room temperature and linear-expansion
coefficient is 20.9.times.10.sup.-6/K in a temperature range of
from room temperature to 200.degree. C. Moreover, the cylinder 31
of the cylinder block 30 comprises a press-fitted sleeve that is
made of cast iron.
[0090] The cylinder head 40 is provided with an intake port 41, and
a discharge port 42. The opening of the intake port 41 is opened
and closed by the cone-shaped head of an intake valve 71 that is
driven by a not-shown intake-side cam. The opening of the discharge
port 42 is opened and closed by the cone-shaped head of a discharge
valve 72 that is driven by a not-shown discharge-side cam.
Moreover, the cylinder head 40 is further provided with a spark
plug 80 in the middle virtually between the intake valve 71 and the
discharge valve 72. In addition, the cylinder head 40 is further
provided with an injector 50, a fuel injection valve, on the side
of the intake port 41. The injector 50 has an opening 51 through
which gasoline (i.e., liquid fuel) being pressurized to
predetermined pressure is sprayed into the cylinder 31 of the
cylinder block 30.
[0091] The piston 10, a piston for in-cylinder fuel-injection type
combustion engine according to the present invention, comprises a
piston head 11, and a piston body 12. The piston 10 is connected
with a connecting rod 60 swingably by way of a piston pin 61. The
piston pin 61 is fitted into pin holes 113 that are bored through
the piston body 12 of the piston 10. The piston head 11 that is
present on the piston 10 is provided with a top ring 112a, a second
ring 112b and an oil ring 112c in the outer periphery. Moreover,
the piston head 11 is provided with a deep-dish-shaped section 111
on the top surface facing the intake port 41. The gasoline is
sprayed from the injector 50 toward the deep-dish-shaped section
111. The inner-wall surfaces of the deep-dish-shaped section 111
(the inside bottom surface, especially) make the "fuel collision
zone" that is recited in the present specification.
[0092] The deep-dish-shaped section 111 of the piston 10 collects
the gasoline, which the injector 50 sprays at around the top dead
center at the time of super fuel-lean burning, around a spark plug
80. Thus, even when an air-fuel ratio is high, an air-fuel mixture
with ignitable concentration is formed around the spark plug 80.
Then, when the spark plug 80 ignites spark discharge between the
gaps, the stratified charge combustion occurs within the combustion
chamber that is formed between the cylinder head 40 and the piston
head 11. On the other hand, at the time of high-load driving, the
engine 1 naturally carries out uniformly-mixed combustion in
stoichiometric region or fuel-rich region, because the injector 50
sprays the gasoline in the intake process during which the piston
10 descends.
[0093] The engine 1 according to an example of the present
invention further comprises a low thermal conductor 20. The low
thermal conductor 20 is cast buried or enveloped in the
deep-dish-shaped section 111 of the piston head 11. Moreover, a
superficial portion 21 of the low thermal conductor 20, namely, one
of the opposite surfaces thereof, is equivalent to the "low
thermally-conductive zone" that is recited in the present
specification. As can be seen from FIG. 1, the superficial portion
21 of the low thermal conductor 20 only forms a part of the
inner-wall surfaces of the deep-dish-shaped section 111, not the
entirety. In other words, the superficial portion 21 appears
limitedly in such a section in the piston head 11 that the
gasoline, which the injector 50 sprays, can mainly collide with or
adhere onto it. Thus, it is possible not only to facilitate the
vaporization of the sprayed gasoline, but also to avoid the
formation of heat spots that cause knocking.
[0094] Moreover, the low thermal conductor 20 comprises a
later-described low thermally-conductive substrate, and a coating
layer 22 being disposed on the low thermally-conductive substrate's
bottom surface. In addition, the coating layer 22 provides a thin
minute-intersticed layer 14 between the low thermal conductor 20's
lower surface and the piston head 11's top surface. Note that the
coating layer 22 and the minute-intersticed layer 14 are not
present independently to each other but they exist in
interdependent or coexistent relationship or form. A process for
manufacturing the piston 10 according to an example of the present
invention will be hereinafter described in detail, piston 10 in
which the low thermal conductor 20 comprising such a coating layer
22 is cast buried or enveloped in the top.
Process for Manufacturing Piston for In-Cylinder Fuel-Injection
Type Internal Combustion Engine
(a) Manufacturing Low Thermally-Conductive Substrate
[0095] A low thermally-conductive substrate that made the low
thermal conductor 20 comprised a sintered workpiece that was made
of Fe--Mn--C system alloy. The sintered workpiece was manufactured
as described below.
[0096] First of all, a raw-material powder was prepared by mixing a
pure Fe powder, a graphite powder and an Fe--Mn alloy powder
uniformly with a rotary mixer. Note that the Fe--Mn alloy powder
comprised 50%-by-mass Mn, and the balance of Fe and inevitable
impurities. The resulting raw-material powder was charged into a
cavity of mold (or molding die) that was made of cemented carbide,
and was then pressure formed into a powder compact with a forming
pressure of 784 MPa using a lubricated-mold warm pressure forming
method. Note that the lubricated-mold warm pressure forming method
had been developed by some of the present inventors and is
disclosed in Japanese Patent Gazette No. 3,309,970.
[0097] The resulting powder compact was sintered at 1,250.degree.
C. for 30 minutes in a sintering atmosphere that was made up of
1-atm N.sub.2. Thus, a low thermally-conductive substrate
comprising a sintered body was manufactured. Note that the sintered
body was made up of an Fe--Mn--C alloy whose Mn content was 25% by
mass and C content was 1% by mass.
(b) Coating Treatment
[0098] A coating dispersion liquid that had been prepared in
advance was coated onto one of the opposite surfaces of the
resultant low thermally-conductive substrate. The coating
dispersion liquid was comprised ethanol (i.e., a dispersant), and a
coating material that was dispersed in the dispersant. The coating
material comprised an alumina powder, and alumina-silica hydrate
(i.e., an alumina-containing clay). Specifically, the alumina
powder exhibited an average particle diameter of 50 .mu.m and an
apparent density of from 0.7 to 1.2 g/cm.sup.3. Moreover, the used
alumina-silica hydrate was "KIBUSHI NENDO" clay. In addition, the
alumina powder was compounded with the alumina-silica hydrate in a
mixing proportion of 4:1 by mass (i.e., alumina powder:
alumina-silica hydrate). Moreover, in the coating dispersion liquid
prepared as above, the coating material was compounded with the
ethanol in a mixing proportion of 3:2 by mass (i.e., coating
material: ethanol).
[0099] The thus prepared coating dispersion liquid was coated with
a brush onto one of the opposite surfaces of the low
thermally-conductive substrate in a thickness of about 0.2 mm
(i.e., an applying step). Note that the low thermally-conductive
substrate had a diameter of .phi. 39 mm and a thickness of 5 mm and
the coating dispersion liquid was coated on the middle of the low
thermally-conductive substrate's one of opposite surfaces that
extended over the region with a diameter of about .phi. 23 mm. The
low thermally-conductive substrate that had underwent the applying
step was held in an air atmosphere whose temperature was
500.degree. C. for 30 minutes to dry the coating dispersion liquid,
thereby forming a coating layer on the one of the opposite surfaces
of the low thermally-conductive substrate (i.e., a drying
step).
[0100] The low thermally-conductive substrate with the coating
layer being formed, namely, a low thermal conductor that is
directed to the piston according to the present invention, was cast
buried or enveloped in a casting by means of gravity casting using
a molten metal of aluminum alloy (i.e., a cast burying or
enveloping step). Note that the used aluminum alloy was an AC8A
alloy in accordance with JIS. Moreover, the molten temperature of
the molten metal was controlled at 780.degree. C.
[0101] Thus, a test specimen was made, test specimen which
comprised the aluminum-alloy cast product and the low thermal
conductor being cast buried or enveloped in the cast product.
Moreover, as a comparative example, another test specimen was made
as well, another test specimen in which the low
thermally-conductive substrate proper that was not subjected to the
above-described coating treatment was cast buried or enveloped in
the aluminum-alloy casting.
[0102] FIGS. 2 and 3 show cross-sectional photographs for
displaying the test specimen and comparative test specimen that
were cut in the longitudinal direction. As can be seen from FIG. 2,
it is ascertained that the test specimen according to an example of
the present invention comprised the aluminum-alloy casting, and the
low thermal conductor which underwent the coating treatment and was
cast buried or enveloped in the aluminum-alloy casting; and that a
thin minute-intersticed layer (or coating layer) with a virtually
uniform thickness was formed between the low thermally-conductive
substrate and the aluminum-alloy casting, namely, the piston body.
The minute-intersticed layer was not an assembly of simple hollows,
but turned into such a state in which the components of the coating
material, that is, the alumina fine particles, remained in or
coexisted with the minute interstices or pores. Note that it is
believed that to what extent the alumina fine particles are present
in the minute-intersticed or coating layer depends on to what
extent the coating treatment has been carried out (for example, how
thick the coating dispersion liquid has been coated) and how the
aluminum-alloy molten metal has been flowed.
[0103] Note however that the low thermally-conductive substrate
proper cohered to or joined with the aluminum-alloy cast product on
the sections of the cast buried or enveloped surface that were free
from the minute-intersticed or coating layer.
[0104] On the contrary, it is apparent from FIG. 3 that, in the
comparative test specimen which comprised the low
thermally-conductive substrate proper that had not undergone the
above-described coating treatment and was then cast buried or
enveloped in the aluminum-alloy cast product, the low
thermally-conductive substrate cohered to or joined with the
aluminum-alloy cast product over the entire cast-buried or
enveloped surface without any minute voids or spaces.
[0105] Having now fully described the present invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
or scope of the present invention as set forth herein including the
appended claims.
* * * * *