BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to a heat-insulating engine structure.
DESCRIPTION OF THE PRIOR ART
[0002] 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. This heat-insulating
engine will be described with reference to Fig. 5 of the accompanying drawings. This
heat-insulating engine 50 includes a cylinder head 53 of a cast metal and a liner
head 51 of a ceramics material fitted into the 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 periophery of the top of the piston body 57 is 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 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.
[0003] 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.
[0004] 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 heat much
from the ceramics member and is heated and expanded to greatly decrease the suction
efficiency.
[0005] Accordingly, 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.
SUMMARY OF THE INVENTION
[0006] It is a principal object of the present invention to provide a heat-insulating engine
which 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
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.
[0007] 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.
[0008] 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 portion
of the ceramics cylinder head is shaped to have a lowered central portion and a raised
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 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.
[0009] 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 head by an heat insulating layer, the surface of 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.
[0010] 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 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.
[0011] It is a still further 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.
[0012] It is a still further object of the present invention to provide a heat-insulating
engine 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 contact with a thin-walled portion disposed on
a piston head through the intermediary of a heat 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.
[0013] 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.
[0014] 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 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 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.
[0015] It is a still further object of the present invention to provide a heat-insulating
engine in which a heat-insulating material interposed 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 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.
[0016] 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
[0017]
Fig. 1 is an axial sectional view of an embodiment 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
Fig. 5 is an axial sectional view of the prior art heat-insulating engine discussed
hereinabove.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] 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 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 to be exposed to combustion gases. To accord with this planar surface of the thin-walled
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 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.
[0019] 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 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 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 alteratively be disposed in parallel with the cylinder axis.).
[0020] Due to this inclined arrangement of the intake valve 21 and due to the 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 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, 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).
[0021] 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- 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
upper end wall 2 of the piston skirt 2 is formed therein with a central mounting 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 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 around 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.
[0022] 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 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
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.
[0023] 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 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.
[0024] Another or second embodiment of the heat-insulating engine according to the present
invention will be described with reference to 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 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 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.
1. A heat-insulating engine structure comprising:
a piston reciprocatingly movable in a cylinder liner and having a planar surface
to be exposed to combustion gases;
a cylinder liner upper portion of a ceramics material disposed above said cylinder
liner;
a cylinder head bottom wall portion integral with said cylinder liner upper
portion and having a raised outer peripheral portion and a lowered central portion;
a cylinder head including a tubular section accommodating said integral cylinder
liner upper portion and said cylinder head bottom wall portion;
said cylinder head bottom wall portion and said cylinder liner upper portion
cooperating to define a combustion chamber;
a fuel injection nozzle disposed substantially centrally of said cylinder head
bottom wall portion and having radially outwardly directed injection orifices;
intake and exhaust valve seats formed in an inclined surface of said cylinder
head bottom wall portion, said inclined surface extending radially upwardly from said
central portion of said cylinder head bottom wall portion to said outer peripheral
portion thereof; and
intake and exhaust valves associated with said intake and exhaust valve seats,
respectively.
2. A heat-insulating engine structure according to Claim 1, wherein said cylinder
liner upper portion has a tubular upper part of substantially square cross-section
and a substantially cylindrical lower part, said combustion chamber including a substantially
square portion defined by said tubular upper part of said cylinder liner upper portion.
3. A heat-insulating engine structure according to Claim 2, wherein said tubular upper
part of substantially square cross-section is smaller than the inner diameter of said
cylindrical lower part.
4. A heat-insulating engine structure according to Claim 2, wherein said tubular upper
part has rounded corners.
5. A heat-insulating engine structure according to Claim 1, wherein said fuel injection
nozzle injects a fuel radially outwardly through said injection orifices into said
combustion chamber.
6. A heat-insulating engine structure according to Claim 1, wherein said cylinder
head bottom wall portion and said cylinder liner upper portion are of an integral
thin-walled structure of a ceramics material.
7. A heat-insulating engine structure according to Claim 1, wherein said cylinder
head bottom wall portion and said cylinder liner upper portion are of an integral
structure of silicon nitride.
8. A heat-insulating engine structure according to Claim 1, wherein said cylinder
head bottom wall portion and said cylinder liner upper portion are of an integral
structure of silicon carbide.
9. A heat-insulating engine structure according to Claim 1, wherein a heat-insulating
layer is disposed between said cylinder head bottom wall portion and said cylinder
and between an outer peripheral surface of said cylinder liner upper portion and an
inner peripheral surface of said cylinder head.
10. A heat-insulating engine structure according to Claim 9, wherein said heat-insulating
layer includes a heat-insulating material made of potassium titanate and the like.
11. A heat-insulating engine structure according to Claim 1, wherein said intake and
exhaust valves are disposed in a generally inverted V arrangement.
12. A heat-insulating engine structure according to Claim 11, wherein said cylinder
head is formed therein with an intake port extending obliquely and radially inwardly
to said intake valve seat.
13. A heat-insulating engine structure according to Claim 12, wherein intake air introduced
through said intake port into said combustion chamber in each suction stroke of the
engine includes a primary flow disposed substantially vertically centrally of said
combustion chamber.
14. A heat-insulating engine structure according to Claim 2, wherein sprays of fuel
injected into said combustion chamber and intake air form a swirl and wherein said
tubular upper part of substantially square cross-section has sides operative to agitate
said swirl whereby the fuel and the air are immediately and uniformly mixed.
15. A heat-insulating engine structure according to Claim 1, wherein said piston includes
a piston skirt having an upper end wall, a piston head portion having a mounting portion
by which said piston head portion is mounted on said upper end wall, a ring of a ceramics
material urged against and secured to an upper surface of said piston skirt, a thin-walled
portion constituting said planar surface and having an outer periphery bonded to said
ring, said piston head portion having an undersurface cooperating with an undersurface
of said thin-walled portion and with a part of an inner peripheral surface of said
ring to define a space, and a heat-insulating material disposed in and filling up
said space.
16. A heat-insulating engine structure according to Claim 15, wherein said thin-walled
portion constitutes said planar surface to be exposed to combustion gases and is made
of a ceramics material having as thin a wall thickness as possible.
17. A heat-insulating engine structure according to Claim 15, wherein the outer periphery
of said thin-walled portion is bonded to an upper part of said ring by a chemical
vapor deposition of a ceramics material.
18. A heat-insulating engine structure according to 15, wherein said piston head has
a planar upper surface.
19. A heat-insulating engine structure according to Claim 15, wherein said heat-insulating
material acts as a structural member which bears a pressure acting on said thin-walled
portion.
20. A heat-insulating engine structure according to Claim 15, wherein said thin-walled
portion and said ring are made of silicon nitride.
21. A heat-insulating engine structure according to Claim 15, wherein said thin-walled
portion and said ring are made of silicon carbide.
22. A heat-insulating engine structure according to Claim 15, the inner peripheral
surface of said ring is formed thereon with a step with which said piston head engages
at its outer periphery, and wherein said piston head portion is secured to said piston
skirt whereby a lower end of said ring is urged against an upper end face of said
piston skirt.
23. A heat-insulating engine structure according to Claim 22, wherein a gasket for
seal is interposed between said lower end of said ring and said upper end face of
said piston skirt.
24. A heat-insulating engine structure according to Claim 15, wherein said mounting
portion of said piston head portion is a mounting hub formed substantially centrally
of said piston head portion, and wherein said mounting hub is fitted into a central
mounting hole formed in said piston skirt.
25. A heat-insulating engine structure according to Claim 24, said piston head portion
and said piston skirt are secured together by a metallic ring forcibly engaged into
and interconnecting annular grooves respectively formed in an outer peripheral surface
of said mounting hub and an inner peripheral surface of said central mounting hole.
26. A heat-insulating engine structure according to Claim 24, wherein a part of said
piston head portion adjacent to said mounting hub and a part of said piston skirt
adjacent to said central mounting hole are urged toward each other with a shock absorbing
member interposed there-between, said shock absorbing member also providing a heat-insulating
function.
27. A heat-insulating engine structure according to Claim 15, wherein said piston
head portion has an undersurface cooperating with an upper surface of the upper end
wall of said piston skirt and a part of an inner peripheral surface of said ring to
define a heat-insulating air chamber.
28. A heat-insulating engine structure according to Claim 15, wherein said piston
head is made of a material having a coefficient of thermal expansion substantially
equal to that of a ceramics material of cermet or metallic material, a high strength
and a high Young's modulus.
29. A heat-insulating engine structure according to Claim 15, wherein said heat-insulating
material is a heat-resisting material of a high porosity such as potassium titanate
whisker, zirconia fiber and so forth.
30. A heat-insulating engine structure according to Claim 15, wherein said piston
skirt has an outer peripheral surface with a piston ring groove formed therein and
provided with a piston pin hole extending diametrically of said piston skirt.