Note: Descriptions are shown in the official language in which they were submitted.
133111~
The present invention relates to a heat-insulating
engine structure.
A heat-insulating engine which makes use of heat-
insulating members and heat-resistant members both made of
a ceramics material has heretofore been known and is
disclosed, for example, in Japanese Un-Examined Patent
Publication No. 59-122,765. Such a heat-insulating engine
includes a cylinder head of a cast metal and a liner head of
a ceramics material fitted into the cylinder head with
positioning rings interposed therebetween. The liner head
constitutes a cylinder head bottom wall portion and an
integral cylinder liner upper portion both of which are
exposed to combustion gases at the highest temperature and
I pressure levels during each cycle of engine operation and
from which heat is removed most during the engine operation.
A cylinder block is disposed under the bottom end of the
liner head with a gasket interposed therebetween. The
cylinder block is fitted with a cylinder liner which
accommodates a reciprocating piston having a piston head of
silicon nitride. The piston head is recessed in its central
area to provide a combustion chamber and has an inwardly
stepped bottom end which serves as means for positioning and
preventing the piston head from being moved relative to a
piston body when the piston head is assembled with the
piston body. A bolt hole is formed in and extends through
the bottom wall of the recess. The outer periphery of the
top of the piston body is shaped to provide an annular
projection which is snugly engaged with the inwardly
stepped bottom end of the piston head. The upper face of
the piston body has an upwardly projecting central portion
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1331119 ~ ~
having a top face engaged with the bottom face of the piston
head. The piston head and body are secured together by a
bolt extending through the bolt hole in the piston head and
through a similar bolt hole in the piston head. Intake and
exhaust valves are disposed adjacent to the cylinder head
bottom wall portion and axially of the cylinder liner.
The heat-insulating engine is not of a structure
which is suited to reduce the thermal capacity as much as
possible, because the ceramics piston head is formed therein
with the recess and, therefore, is required to have a
substantial thickness so as to assure a sufficient
mechanical strength. The intake and exhaust valves are
disposed axially of the cylinder liner in compliance with
the structure of the piston head. The cylinder head bottom
wall portion is of a flat design, with the result that air
sucked into the engine cylinder flows radially outwardly of
the intake valve and, accordingly, is apt to receive heat
from the upper part of the cylinder liner as well as from
the cylinder head bottom wall portion. Thus, the cylinder
head bottom wall portion is not so structured as to swirl
the air for the purpose of agitating the air.
It is very difficult to fully obtain the heat-
insulating characteristics of a heat-insulating engine which
makes use of ceramics material as heat-insulating or heat~
resistant material. The engine is of the structure which
exposes the ceramics members to combustion gases at a high
temperature, so that the ceramics members are subjected to
thermal shocks, which raises a problem in terms of
mechanical strength. In the case where the thickness of a
ceramics member is increased for the purpose of heat-
insulation, the thermal capacity of the member if increased,
with a disadvantageous result that air sucked into an engine
cylinder during an intake stroke of the cylinder receives
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heat much from the ceramics member and is heated and
expanded to greatly decrease the suction efficiency.
According, it has been desired to improve the
suction efficiency and the cycle efficiency of heat-
insulating engines. In addition, it has also been demanded
in Diesel engines to assure that a fuel injected from a fuel
injection nozzle is quickly and uniformly mixed with air by
virtue of swirl formed in a combustion chamber.
According to the present invention, there is
provided a heat-insulating engine structure comprising:
- a piston reciprocatingly movable in a cylinder
liner; the piston having a piston skirt portion, a piston
head portion fixed to the piston skirt portion and having a
planar upper surface, a heat insulating material provided on
the upper surface of the piston head portion, and a planar
surface provided on the upper surface of the heat-insulating
material and exposed to combustion gases;
- a cylinder head bottom wall portion which is of
a ceramics material, is integral with the cylinder liner
upper portion, and extends upwardly from its center to
periphery so as to have a raised outer periphery portion
all over the circumference of the portion and a lowered
central portion;
- a cylinder head including a tubular section
accommodating the integral cylinder liner upper portion and
the cylinder head bottom wall portion;
- the cylinder head bottom wall portion and the
cylinder liner upper portion cooperating to define a
combustion chamber;
- a fuel injection nozzle disposed substantially
centrally of the cylinder head bottom wall portion and
having radially outwardly directed injection orifices;
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- intake and exhaust valve seats formed in an
inclined surface of the cylinder head bottom wall portion,
the inclined surface extending radially upwardly from the
central portion of the cylinder head bottom wall portion to
the outer peripheral portion thereof; and
- intake and exhaust valves associated with the
intake and exhaust valve seats, respectively.
The principal object and the further objects of
the present invention are summed up hereafter.
It is a principal object of the present invention
to provide a heat-insulating engine which 7
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1331119
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is structured to improve the suction efficiency
and the cycle efficiency of the heat-insulating
engine as well as to assure that fuel injected
from a fuel injection nozzle is immediately and
uniformly mixed with intake air, thereby to solve
the problems pointed out above. More specifically, ;~
in order to improve the suction efficiency and
the cycle efficiency, the top face portion of a
piston head of the engine which is exposed to
combustion gases is formed of a wall of a ceramics
material having as small a thickness as possible
to minimize the thermal capacity of the piston top
face portion. Reduction in the thicknesses of the
ceramics wall portions exposed to combustion gases
and the resultant decrease in the thermal
capacities thereof assure that walls defining a
combustion chamber can better follow variation in ; ;
combustion gas temperature. As compared with the
case in which the combustion chamber walls have
greater thicknesses, the amplitude of the
temperature variation in the combustion chamber
walls having smaller thicknesses is increased to
advantageously decrease the difference in
temperature between the combustion gases and the
ceramics material of the combustion chamber walls
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13311~9
with a resultant decrease in the heat transfer to
thereby reduce the heat transferred from the
combustion chamber walls to the air introduced
into the combustion chamber. The reduction in
the heat transfer to the intake air is effective
to prevent undue expansion of the intake air and,
thus, assure a smooth flow of air into the
combustion chamber, whereby the suction efficiency
and the cycle efficiency are greatly improved. -~
It is another object of the present invention
to provide a heat-insulating engine structure in
which the top wall portion of a piston, which is
exposed to combustion gases, is of a planar design
that does not define any combustion chamber and,
instead, a combustion chamber is defined in the
bottom wall portion of a cylinder head. This is
because, in order to reduce the thickness of the
top wall portion of the piston, it is most preferred ~;
for the top wall portion of the piston to have such
a planar configuration.
It is a further object of the present invention
to provide a heat-insulating engine structure in
which, in order that a combustion chamber may be
formed on the side of the cylinder head, rather
than on the side of the piston, the bottom wall
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13311~
portion of the ceramics cylinder head is shaped
to have a lowered central portion and a raised
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outer peripheral portion and cooperates with an
integral ceramics cylinder liner upper portion to
define the combustion chamber. In addition, the
cylinder head bottom wall portion has inclined
surfaces extending radially upwardly from the
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central portion to the outer peripheral portion
and is provided with intake and exhaust valve seats
formed in the inclined surfaces. A fuel injection
nozzle is disposed substantially centrally of the
cylinder head bottom wall portion, so that the
above-mentioned combustion chamber is shaped to
accommodate the pattern of jets of fuel injected
by the fuel injection nozzle. Thus, the injected
fuel can be immediately agitated with intake air ~
and thus uniformly mixed therewith due to an ~ -
agitating flow produced in the combustion chamber.
It is a still further object of the present
invention to provide a heat-insulating engine
structure in which a cylinder head bottom wall
section and a cylinder liner upper portion which
cooperates therewith to define a combustion
chamber are thermally insulated from the cylinder
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1331119
a piston which is exposed to combustion gases, -
i.e., a thin-walled piston top wall portion, is
thermally insulated from a piston head by a heat
insulating layer, and the cylinder liner upper
portion, the cylinder head bottom wall portion and -~
the piston top surface portion are designed to ;~
have as small thicknesses as possible to minimize
their heat capacities as well as to provide the
engine with highly improved heat-resisting
characteristic, heat-insulating characteristic,
anti-deformation characteristic and anti-corrosion
characteristic.
It is a still further object of the present
invention to provide a heat-insulating engine in
which intake and exhaust valve seats are formed in
radially upwardly inclined surfaces of cylinder
heat bottom wall section such that intake and
exhaust valves are disposed in an inverted-V
arrangement and, more particularly, the primary flow
of air introduced into the combustion chamber when
the intake valve is opened is disposed
substantially centrally of the combustion chamber
and, thus, of a cylinder bore to reduce the
possibility that the air flowing into the
combustion chamber is brought into contact with
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the inner surface of a heated upper portion of a
cylinder liner whereby the transfer of heat from ~ .
the cylinder liner upper portion to the air is ~::
decreased to minimize the expansion of the air to
thereby improve the suction efficiency of the
engine.
It is a still furthér object of the present
invention to provide a heat-insulating engine in
which a cylinder liner which defines a combustion
chamber therein has a lower cylindrical portion
and an upper tubular portion of a substantially :~.
square cross-section having a non-circular inner
peripheral configuration which is effective to
destroy the swirl formed in the combustion chamber
to cause an agitation which is effective to assure ~.. :
that the fuel injected by a fuel injection nozzle :
is immediately and uniformly mixed with intake .
air in a zone adjacent to the piston top dead ~ .
center. : j.
It is a still further object of the present
invention to provide a heat-insulating engine
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structure in which the primary flow of intake air
is disposed centrally of a combustion chamber and,
thus, of a cylinder with a resultant increase in
the quantity of intake air that is brought into ~
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contact with a thin-walled portion disposed on a
piston head through the intermediary of a heat
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insulating material and exposed to combustion gases,
and in which the thin-walled portion is structured
to have a very small thermal capacity so as to
eliminate decrease in the suction efficiency
whereby the suction efficiency and the cycle
efficiency of the engine are improved.
It is a still further object of the present
invention to provide a heat-insulating engine in
which a fuel injection nozzle is disposed ~
substantially centrally of a cylinder head bottom :
wall portion and a combustion chamber is shaped
to accommodate the loci or pattern of jets of
fuel injected from a fuel injection nozzle to
reduce the transfer of heat to the inejcted fuel
and the intake air in the combustion chamber so
that expansion of the air can be suppressed and
the injected fuel can be well mixed with the air
to ensure a good combustion.
It is a still further object of the present
invention to provide a heat-insulating engine in
which a piston has a piston head portion of cermet
and a thin-walled portion of a ceramics material
having a coefficient of thermal expansion
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substantially equal to that of cermet to provide a
reliable connection between the two portions, in
which the piston head portion of cermet is highly
rigid and hardly deformed even by a high level of :
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pressure to assure a stable connection between the
piston head portion and the piston thin-walled ;
portion, to establish a reliable gas-seal at the :~
boundary therebetween and to avoid any strength
problem which would otherwise be adversely affected -
by thermal shock, in which the heat-resisting
characteristic, anti-deformation characteristic
and anti-corrosion characteristic and so forth of
the piston are improved, and in which the pressure
exerted to the thin-walled portion of the piston
in each combustion stroke can be borne through a :::
heat-insulating material by the piston head ;.~ :
portion. ~ ;
It is a still further object of the present
invention to provide a heat-insulating engine in -~
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which a heat-insulating material interposed .~
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between a thin-walled portion of a piston and a
piston head portion is made of potassium titanate
whisker, zirconia fiber or of a mixture of these
materials and glass fiber to provide a highly ~;
efficient heat-insulator against the heat produced .
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in an associated combustion chamber to eliminate
leakage of thermal energy from the combustion
chamber through the piston whereby the thermal
energy is trapped inside the combustion chamber
to assure that the thermal energy can be collected
by means of an energy-collector disposed at a
downstream point of the flow of engine exhaust
gases.
~ The above and other objects, features and
¦ advantages of the invention will become more
apparent from the following description with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an axial sectional view of an
embodlment of a heat-insulating engine according
to the present invention;
Fig. 2 is a cross-sectional view of the engine
taken along line II-II in Fig. 1;
Fig. 3 is an axial sectional view of another
embodiment of the heat-insulating engine according
to the present invention;
Fig. 4 is similar to Fig. 3 but illustrates
a flow of air in a combustion chamber; and
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Fig. 5 is an axial sectional view of the
prior art heat-insulating engine discussed
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13311~
hereinabove.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to Fig. 1 showing the ;
structure of a heat-insulating engine embodying
the present invention, the engine 50 is generally
designated by reference numeral 10 and constituted
mainly by a piston 20 which reciprocates within a
I cylinder liner 34 fitted into a cylinder block 38
¦ and formed by a piston head portion 1 and a piston
skirt portion 2 of a metal, a liner head 30 fitted
in a metallic cylinder head 33 with a heat-
insulating layer interposed therebetween and made
of a ceramics material such as a silicon nitride or
a silicon carbide, a fuel injection nozzle 25
disposed centrally of the liner head 30, and an ;
intake valve 21 and an exhaust valve 27 both
disposed adjacent to the undersurface of the liner
head 30. A flat or planar and thin-walled portion
5 of a ceramics material is mounted, via a heat-
insulating material 3, on the side of the piston -~
head portion 1 which is adjacent to a combustion
chamber to be described. The thin-walled portion ~
5 is shaped to provide a planar surface which is l ;;
to be exposed to combustion gases. To accord ~-
with this planar surface of the thin-walled
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133~119 ~
portion 5, the liner head 30 is shaped to define
a combustion chamber 15 having a lowered part and
a raised part which are disposed adjacent to the
central and outer peripheral zones of the cylinder
and thus will be termed ~lowered central part~
and "outer peripheral part", respectively. The
liner head 30 is constituted by a cylinder liner
upper portion 23 disposed above the cylinder liner ~-
34 and a cylinder head bottom wall portion 22
integral with the cylinder liner upper portion 23.
The cylinder head bottom wall portion 22 is shaped
to have a raised outer peripheral part and a
lowered central part to provide an inclined
surface extending radially upwardly from the
lowered central part to the raised outer peripheral
part. The heat-insulating engine 10 equipped with
the liner head 30 of the described structure is
of the structure which is suited to insulate heat
particularly during a heat-producing period when
a combustion is most active. The combustion
chamber 15, which is defined by the cooperation of
the liner head 30 and the thin-walled element 5
of the piston head portion 1, both having the
structures described above, is most suited to a
heat-insulating engine and presents a configuration
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or profile resembling the shape of a shallow dish
providing a radially outwardly increasing volume.
The piston is provided with piston rings 39
received in piston ring grooves and has a pin hole
41 for a piston pin. -~,
Fig. 2 is a cross-sectional view taken along
line II-II in Fig. 1. The cylinder liner upper
portion 23, which cooperates with the piston to
define the combustion chamber 15, has an upper
tubular part 26 of a generally square cross-section
and a lower cylindrical part 28 of a circular
cross-section. The square tubular part 26 is ;~
smaller in diameter than the cylindrical part 28.
The square tubular part 26 has corners each of
which, from the view point of the flow of the
fluid, is preferably rounded with a radius of
curvature equal to about from 1/2 to 1/3 the radius
of the cylindrical part. This design is effective
to assure that the four sides of the square cross~
section of the square tubular part 26 are
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operative to destroy a swirl produced within the
combustion chamber 15, or in other words, to
break the swirl to establish an agitation by which
injected fuel and intake air are very quickly and
uniformy mixed in a zone adjacent to the top dead
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1331~1~
center of the piston to thereby facilitate a good
combustion. The outer surfaces of the liner head ~
30 are thermally insulated by a heat-insulating ~ ~;
gasket 29 of potassium titanate and by a heat-
insulating layer 24. Thus, the liner head 30
itself can be designed to have a reduced wall
thickness and, thus, a small thermal capacity.
As will be clearly seen in Fig. 2, moreover, the
intake valve 21 and the exhaust valve 27 are so
disposed as to cooperate with intake and exhaust
valve seats formed in the inclined surface of
the cylinder head bottom wall portion 22 which
surface extends between the central and outer
peripheral portions thereof. More specifically,
the cylinder head bottom wall portion 22 has its
major part extending radially outwardly and
upwardly to provide the above-mentioned inclined
surface, as shown in Fig. 1, so that the intake
and exhaust valves 21 and 27 associated with the
intake and exhaust valve seats formed in the
inclined surface are disposed in an inverted
V-shape arrangement (but the valves may
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alteratively be disposed in parallel with the -
cylinder axis.).
Due to this inclined arrangement of the
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intake valve 21 and due to tne shape of an intake
port 31 extending radially inwardly and obliquely
from outside the combustion chamber 15 to the
cylinder head bottom wall portion 22, the intake
air sucked into the combustion chamber has its
primary flow directed substantially vertically of
the engine towards the center of the combustion
chamber (refer to the air flow shown by arrows A
in Fig. 4 and described later). Accordingly, the
intake air is hardly brought into contact with the
inner surface of the liner head 30 which is at a
high temperature during each intake stroke of the
engine, with a result that the heat transfer from
the liner head to the intake air is advantageously
reduced to minimize the thermal expansion of the
air and, thus, to eliminate reduction in the
suction efficiency which would otherwise be caused.
In this case, the amount of intake air would be
increased which is brought into contact with the
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thin-walled portion 5 of the piston head 1, i.e., -
the top face of the piston. Such increase,
.,
however, will not give rise to decrease in the
suction efficiency because the thin-walled portion
5 of the piston 20 is structured to have a very
small thermal capacity. On the other hand,
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1331119
because the intake valve 21 and the exhaust
valves 27 are disposed in the combustion chamber
15, these valves do not interfere with the piston
20 even if the valves were accidentally opened
when the piston 20 is in its top dead center,
thereby to assure a reliable and safe engine
operation. In addition, the fuel injection nozzle
25 has its injection orifices directed radially
outwardly. Thus, the jets of fuel injected through
the injection orifices are directed in parallel
with and radially outwardly of the thin-walled
portion 5 of the piston head 1. It will therefore
be appreciated that the combustion chamber 15, which
is partly defined by the liner head 30, is shaped
to accommodate the loci of the jets of fuel injected
by the fueL injection nozzle 25 (see the pattern
of the jets of fuel shown by arrows B in Fig. 1).
Then, the piston 20 will be described. This ~-
piston 20 is constituted mainly by a piston skirt ;
32 having an upper end wall 32, the above-mentioned
piston head portion 1 which has a mounting hub 4
by which the piston head portion is mounted on the
skirt upper end wall 32, a ring 6 of a ceramics
material secured to the upper face of the skirt
~ 2 in pressure-contact therewith, the above-
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1331119 ~:mentioned thin-walled portion 5 of a ceramics ~ : :
material having an outer periphery bonded to the
ring 6 and providing a surface to be exposed to
combustion gases, and a layer of a heat-insulating ~
material 3 interposed between the piston head ~;
portion 1 and the thin-walled portion 5. The
piston head portion 1 has the mounting hub 4 in
its center and is made of a material, such as, :
for example, cermet or a metal, which has a
thermal expansion coefficient substantially equal -.
to that of a ceramics material, a high strength
and a relatively high Young's modulus. The piston
head 1 itself is not formed therein with any
combustion chamber and is planar or flat in its ;~ ; :
side adjacent to the combustion chamber 15. The ~ ::
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upper end wall 2 of the piston skirt 2 is formed
therein with a central moùnting hole 12 for
receiving the mounting hub 4 of the piston head
portion 1. The piston head mounting hub 4 is :
fitted into the mounting hole 12 in the piston :-
skirt upper end wall 32 with a metallic ring 11 ~ ;
press-fitted into and interconnecting an annular
groove 14 in the outer peripheral surface of the :
mounting hub 4 and an annular groove 13 in the . .
inner peripheral surface of the mounting hole 12
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so that the piston head portion 1 is secured to
the piston skirt 2. A shock absorbing member 8
formed of a heat-insulating material is interposed
and pressed between the piston head portion 1 aLound
the mounting hub 4 and the piston skirt 2 around
the central mounting hole 12 and acts also as a
heat-insulator. A heat-insulating air chamber 9
is defined by the cooperation of the undersurface
of the piston head portion 1, the upper surface of
the piston skirt 2 and the inner peripheral surface
of the ring 6. It is to be understood that the
thin-walled portion 5 of the piston 20 is so ;~ ~
disposed on the piston head portion 1 as to face ~`
the combustion chamber 15, i.e., exposed to
combustion gases, with the heat insulating material
3 interposed between the thin-walled portion 5 and ^~
the piston head portion 1. The thin-walled portion
5 is made of a ceramics material such as silicon
nitride or silicon carbide and has a thickness of
: '. , .:
about 1 mm or less.
The outer periphery of the thin-walled portion
5 is bonded to the ring 6 which is made of a similar
material. The bonding between the thin-walled
portion 5 and the ring 6 is achieved by, for
example, a chemical vapor deposition of a ceramics
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~33~
material at a junction 18 therebetween. The ~ .
inner peripheral surface of the ring 6 is formed
thereon with an annular shoulder or step 16. The ~:~
piston head 1 has an outer periphery 17 which is
fitted into the ring 6 and disposed in engagement
with the annular step 16. The upper surface of the
piston head portion 1, the undersurface of the
thin-walled portion 5 and a part of the inner -
peripheral surface of the ring cooperate together ;.
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to define a space which is filled with the heat~
insulating material 3. This heat-insulating
material 3 is made from potassium titanate whisker,
zirconia fiber or the like and acts not only as a :
heat-insulating layer but also as a structural
member which bears the pressure exerted to the
thin-walled portion 5 and produced when a -:~:
combustion takes place in the combustion chamber :
15.
Because the piston head 1 is urged against -:
and connected to the piston skirt 2, the outer
periphery 17 of the piston head portion 1 is urged ~:
against the annular step 16 on the ring 6 which
in turn is urged against the outer periphery of
the upper surface of the piston skirt 2. The
junction between the ring 6 and the piston skirt
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2 is sealed by a gasket formed by a carbon seal 7
interposed therebetween. An axial sealing force
is exerted to and acts on the carbon seal 7
because the piston head portion 1 is urged against
and secured to the piston skirt 2. It is a
requirement for the structure of the piston 20 that
the heat-insulating material 3 uniformly receives
a compression force produced by a combustion. So
as to comply with this requirement, the surface of
the piston head 1 adjacent to the combustion ;
chamber and the thin-walled ceramics portion 5 are
designed to be planar.
Another or second embodiment of the heat-
insulating engine according to the present
invention will be described with reference to ~1
Figs. 3 and 4. The heat-insulating engine of the
second embodiment is distinguished from the heat-
insulating engine of the embodiment described with
reference to Fig. 1 only in the shape of the liner
head constituted by the cylinder head bottom wall
portion and the cylinder liner upper portion. The
portions of the second embodiment which are the
same as those of the first embodiment are
designated by the same reference numerals and
thus are not described hereinunder for the purpose
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13311~9
of simplification of the description. The heat~
insulating engine of the second embodiment is
generally designated by reference numeral 40 and
has a liner head 35 which constitutes a cylinder
head bottom wall portion 37 and an integral
cylindrical liner upper portion 36. The cylinder
head bottom wall portion 37 of the heat-insulating
engine 40 is shaped to provide a raised outer `~
peripheral portion and a lower central portion as ;~
in the cylinder head bottom wall portion 22 of the
heat-insulating engine 10 of the first embodiment.
Thus, the cylinder head bottom wall portion 37
provides an inclined surface extending radially
outwardly and upwardly from the central portion to
the outer peripheral portion. Accordingly, the
combustion chamber 15 which is defined by the .
cooperation of the cylinder head bottom wall
portion of the described shape and the flat thin-
walled portion 5 of the piston head 1 is most
suited for a heat-insulating engine and resembles
the shape of a shallow dish providing a radially `
outwardly increasing volume. With respect to the~`
intake valve 21, the fuel injection nozzle 25 and ;~
the piston 20, the engine 40 of the second
embodiment is entirely the same as the engine 10
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13311~9
of the first embodiment. The flow of air introduced in each
intake stroke of the heat-insulating engine 40 is shown by
arrows A in Fig. 4. The flow of intake air into the
combustion chamber 15 and the directions of the jets of fuel
injected from a fuel injection nozzle 25 into the ~
combustion chamber are also entirely the same as those in ;
the first embodiment.
The heat-insulating engine 50 of the prior art
shown in Fig. 5 includes a cylinder head 53 of a cast metal
lo and a liner head 51 of a ceramics material fitted into the 1
cylinder head with positioning rings 66 and 67 interposed
therebetween. The liner head 51 constitutes a cylinder head
bottom wall portion 63 and an integral cylinder liner upper
portion 64 both of which are exposed to combustion gases at
the highest temperature and pressure levels during each
cycle of engine operation and from which heat is removed
most during the engine operation. A cylinder block 69 is ~-
disposed under the bottom end of the liner head 51 with a
gasket 65 interposed therebetween. The cylinder block 69 is
fitted with a cylinder liner 52 which accommodates a
reciprocating piston having a piston head 54 of silicon
nitride. The piston head is recessed in its central area,
as shown at numeral 55, to provide a combustion chamber 62
and has an inwardly stepped bottom end 56 which serves as
means for positioning and preventing the piston head 54 from
being moved relative to a piston body 57 when the piston
head is assembled with the piston body. A bolt hole 68 is
formed in and extends through the bottom wall of the recess
55. The outer periphery of the top of the piston body 57 is
. 30 shaped to provide an annular projection 58 which is snugly
engaged with the inwardly stepped bottom end of the piston ;
head 54. The upper face of the piston body has an upwardly
projecting central portion 59 having a top face engaged with
the bottom face of the piston head 54. The piston head and
24
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body 54 and 57 are secured together by a bolt 60 extending
through the bolt hole 68 in the piston head and through a
similar bolt hole in the piston head 57. Intake and exhaust
valves 61, only one of which is shown, are disposed adjacent
to the cylinder head bottom wall portion and axially of the
cylinder liner 52. ~ :
I The heat-insulating engine 50 is not of a
¦ structure which is suited to reduce the thermal capacity as :~:
much as possible, because the ceramics piston head 54 is
formed therein with the recess 55 and, therefore, is
required to have a substantial thickness so as to assure a
sufficient mechanical strength. The intake and exhaust
valves 61 are disposed axially of the cylinder liner 52 in
compliance with the structure of the piston head 54. The
cylinder head bottom wall portion 63 is of a flat design,
with the result that air sucked into the engine cylinder
flows radially outwardly of the intake valve and, :
accordingly, is apt to receive heat from the upper part of
the cylinder liner 64 as well as from the cylinder head
bottom wall portion 63. Thus, the cylinder head bottom wall
portion is not so structured as to swirl the air for the
purpose of agitating the air.
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