Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention rël;ates generally to evaporable
foam patterns for use in casting an engine block of a
two-cycle engine.
Cast metal engine blocks for multi-cylinder,
in-line, two-cycle engine generally consist of a cylinder
block and three separate cast covers, including two water
passage covers and an exhaust passage cover, all of which
are attached to the cylinder block by bolts. To provide
the connection between the covers and the cylinder block,
the cylinder block is formed with a series of enlarged
lands or bosses, which are drilled or cast and tapped to
receive bolts, and similarly mating holes are drilled or
cast in the covers. In addition, the mating surfaces
between the covers and the cylinder block are machined and
the covers are attached to the cylinder block through
gaskets and bolts. The gasketed surfaces must be provided
with a substantial width to receive the gaskets and
prevent leakage between the components.
In the fabrication of a conventional
three-cylinder, two-cycle engine, as many as 100
fasteners, such as bolts, screws, and the like, are
required to attach the covers to the cylinder block and
substantial time and labor is required in machining the
interfaces, tapping and drilling holes, applying gaskets
and bolting the covers to the block. The intensive labor
that is required is a substantial factor in the overall
cost of the engine.
Furthermore, the requirement for providing bosses
on the cylinder block and the increased width of the
gasket surfaces adds to the overall weight of the engine.
In evaporable foam casting processes, a pattern
is formed of an evaporable foam material, such as
polystyrene. The foam pattern is substantially identical
in configuration to the cast metal part to be produced,
subject to shrinkage and/or other conditions of the
casting process. The foam pattern is placed in a mold and
surrounded with a finely divided medium, such as sand,
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which also fills the cavatles in the pattern. When molten
metal is introduced into the mold, the molten metal will
heat and vaporize the pattern, with the vapor passing into
the interstices of the sand, while the molten metal will
fill the voids created by vaporization of the foam to
provide a cast metal part having substantially the same
configuration as the foam pattern. Evaporable foam
casting processes have particular advantage when casting
parts of unusual or complex contours.
The present invention provides an evaporable foam
pattern to be used in casting a two-cycle metal engine
block, the assembled pattern comprising a crankcase end
and a head end, said pattern including at least one
cylinder having an end open to the crankcase end of said
pattern and the opposite end enclosed by a head, exhaust
passage means connecting said cylinder to the exterior of
the pattern, said cylinder having at least one
longitudinally extending transfer passage, water cooling
passage means bordering said cylinder and said exhaust
passage means, said pattern composed of a plurality of
separate evaporable foam sections including a first foam
section extending from said crankcase end to the
corresponding end of said transfer passage, a second
pattern section extending from said end of said transfer
passage to a location intersecting said exhaust passage,
said pattern also including a third section extending from
said exhaust passage to said head end including said head,
a fourth pattern section disposed at the head end of the
pattern and enclosing the portion of said water cooling
passage means bordering said cyliner, and a fifth pattern
section connected to corresponding sides of said second
and third sections and enclosing the side of said water
cooling passage means bordering said exhaust passage means.
The assembled foam pattern also includes a
network of water cooling passages which surround the
cylinders, as well as the exhaust manifold. Water is
introduced into the cooling passages through an inlet
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passage formed in a side surface of the pattern and is
discharged from the cooling passages through a discharge
passage located adjacent the inlet passage.
Preferably, the evaporable foam pattern is formed
of a plurality of foam sections which are joined together
by glue or adhesive to provide the assembled pattern.
More particularly, the preferred pattern includes a first
pattern section which extends from the crankcase end of
the pattern to the lower ends of the transfer passages,
and a second section extends from the lower ends of the
transfer passages to a location intersecting the exhaust
passages of the cylinders.
A third pattern section extends from the exhaust
passages to the heads of the cylinders and a fourth
section encloses the outer ends of the cooling passages
that surround the cylinders.
The assembled pattern also includes a fifth
pattern section that is connected to the second and third
pattern sections and includes water passages that border
the exhaust manifold passage.
The interfaces or parting lines between the
first, second, third and fourth pattern sections
preferably are parallel to each other and extend normal to
the axes of the cylinders, while the parting line between
the fifth section and the second and third sections
extends parallel to a plane passing through the axes of
the cylinders.
The five separate pattern sections may be joined
together along the parting lines by a glue or adhesive,
such as conventionally used in evaporable foam casting
processes, to provide the assemble pattern.
In casting, the pattern is placed in a mold and
the region between the pattern and the mold is filled with
a flowable material, such as sand, which also fills the
cavaties in the pattern. Molten metal such as an aluminum
alloy, is introduced to the pattern via a sprue and the
heat of the molten metal will vaporize the pattern. The
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resulting vapor is entra`pp~d within the interstices of the
sand, while the molten metal will fill the voids created
by vaporization of the foam pattern to provide a cast
metal part which is identical in configuration to the
pattern.
Through use of the pattern of the invention, the
entire engine block can be integrally cast as a single
unit, thereby eliminating the machining, drilling and
tapping operations that have been practiced in the past
when using separate covers and a cylinder block.
As a further advantage, it is not necessary to
provide bosses or enlargements of the cylinder block for
tapped holes, nor is it necessary to provide wide
gasketing surfaces, and this provides an appreciable
savings in overall weight of the engine. Elimination of
gaskets and covers eliminates a significant source of
leakage paths.
As the covers are cast integrally with the
cylinder block, the invention elininates as many as 100
fasteners, i.e. bolts and screws, as previously used in
connecting the covers to the cylinder block.
The use of the evaporable foam pattern provides
greater design flexibility and enables more uniform wall
thicknesses to be obtained, thereby providing more
effective heat transfer and reducing the overall weight of
the engine.
Other features and advantages will appear in the
course of the following description of a preferred
embodiment of the invention taken together with the
accompanying drawing wherein;
Fig. 1 is a bottom view of the evaporable foam
pattern used in casting a three-cylinder in-line two-cycle
engine;.
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Fig. 2 is a transverse section of the pattern;
Fig. 3 is a longitudinal section of the pattern;
Fig. 4 is a section taken along line 4-4 of Fig. 2; and
Fig. 5 is a section taken along line 5-5 of Fig. 2.
The drawings illustrate an evaporable foam pattern 1
formed of a material, such as polystyrene, to be used in
casting a multi-cylinder, in-line, two-cycle engine block.
While the drawings illustrate an engine block having three
in-line cylinders, it is contemplated that the invention can
be utilized in casting a two-cycle engine block having at
least one or more cylinders.
The evaporable foam pattern is substantially identical
in shape to the cast metal engine block and, therefore, the
description of the components of the foam pattern will
correspond to that of the cast engine block.
Pattern 1 includes a crankcase end 2 and a head end 3,
and in normal usage of the engine, the crank shaft will
extend vertically.
Pattern 1, as assembled, defines three cylinders 4 each
having an end that opens at the crankcase end 2 of the
pattern. As shown in Fig. 2, an exhaust passage 5
communicates with each cylinder 4 and is located generally
mid-way of the length of the cylinder. The exhaust passages
5, in turn, are connected to an exhaust manifold passage 6,
as best shown in Fig. 2 and the exhaust manifold passage 6
terminates in an exhaust outlet 7 located in a side of the
pattern.
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The two-cycle engine also includes three longitudinal
transfer passages 8, 9 and lO; which are associated with each
of the cylinders 4. As best illustrated in Fig. 4, each
transfer passage 8 is provided with a pair of curved or
radiused ends 11 and 12, and similarly each transfer passage
9 is provided with curved ends 13 and 14.
Each transfer passage lO is formed with curved or
rounded ends 15 and in addition the end of the transfer
passage lO facing the head of the cylinder is provided with a
pair of fingers 17 which divide the passage into three
sections, as shown in Fig. 4.
As illustrated in Figs. 3 and 4, the outer end of each
cylinder 4 is enclosed by a dome-shaped head 18 and a hole 19
is formed in the head of each cylinder to receive a spark
plug.
Water cooling passages 20 surround the cylinders 4 and a
cooling passage 21 also surrounds the exhaust manifold
passage 6. Cooling water is introduced to the passages 20
and 21 through a water inlet passage 22 which opens on the
side of the block adjacent the exhaust outlet 7, and water is
withdrawn from the cooling passages through a water outlet
passage 23, which is similarly located adjacent the exhaust
outlet 7 in a side of the block.
In accordance with the invention, pattern l is composed
of five separate evaporable foam sections which are joined
together along interfaces or parting lines. More
particularly, the pattern l includes a crankcase pattern
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section 25, a central pattern section 26, a head pattern
section 27, a head cover pattern section 28, and a water
passage cover section 29.
As best shown in Fig. 3, the crankcase section 25
extends from the crank case end 2 of the pattern to a
location at the lower ends of the transfer passages 8, 9 and
10, and is joined to the central section 26 along a parting
line or interface A. As shown in Fig. 4, the lower ends of
transfer passages 8 and 9 are curved or rounded and the
parting line A is located at the tangent point between the
radius of curvature and the longitudinal wall of the transfer
passage.
Central section 26 is joined to head section 27 at a
parting line or interface B, and the parting line B, as shown
in Figs. 4 and 5, intersects the cooling water passages 20,
as well as the exhaust passages 5. As shown in Fig. 5, the
upper end of the exhaust passage 5 is curved or rounded and
the parting line is located at the point of tangency of the
radius of curvature with the longitudinal wall bordering the
exhaust passage.
With this construction, the head 18 of each cylinder is
located in the same foam section piece as the upper end of
the exhaust passage 5 and, therefore, the critical tolerance
between the head 18 and the exhaust passages will be
maintained in order to provide the desired flow of combustion
products across the head and into the exhaust passage.
The head cover section 28 is joined to the head section
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27 along the parting line C and the section 28 encloses~the
cooling passages 20 that surround each of the cylinders 4.
As best shown in Fig. 3, the water passage cover section
29 is joined to the sections 26 and 27 along a parting line D
and serves to close off the water inlet and outlet passages
22 and 23, as well as enclosing the exhaust manifold water
cooling passage 21. The parting line D is located normal to
parting lines A, B and C and is parallel to a plane extending
through the axes of the three cylinders 4.
In assembling the pattern 1, the individually cast foam
sections 25-29 are attached together along the parting lines
by use of a glue or adhesive normally employed in evaporable
foam casting processes. The glue is the type that will be
vaporized by the heat of the molten metal and the vapor from
vaporization of the glue will be trapped in the surrounding
sand along with the vapor generated by evaporation of the
foam pattern, so that no adhesive residue will be present in
the cast metal part.
Through the use of the evaporable foam pattern of the
invention, the engine block can be cast as a single integral
part, thereby eliminating the machining, drilling and tapping
operations that had been used in the past when employing
separate covers along with the cast cylinder block.
Furthermore, the invention eliminates the need for providing
enlarged bosses or lands on the cylinder block that would be
subsequently drilled and tapped for attachment of covers and
similarly eliminates the need for wide gasketing surfaces.
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This substantially reduces the overall weight of the engine
and the material cost.
In addition, the invention provides greater design
flexibility and enables the cylinder walls and exhaust
passage walls to have a substantially uniform thickness to
obtain better heat transfer, as well as reducing the weight
of metal to be utilized.
