U.S. patent application number 16/556106 was filed with the patent office on 2020-01-16 for multi-part piston construction for an opposed-piston engine.
This patent application is currently assigned to ACHATES POWER, INC.. The applicant listed for this patent is ACHATES POWER, INC.. Invention is credited to RYAN G. MACKENZIE.
Application Number | 20200018256 16/556106 |
Document ID | / |
Family ID | 62002509 |
Filed Date | 2020-01-16 |
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United States Patent
Application |
20200018256 |
Kind Code |
A1 |
MACKENZIE; RYAN G. |
January 16, 2020 |
MULTI-PART PISTON CONSTRUCTION FOR AN OPPOSED-PISTON ENGINE
Abstract
A piston for an internal combustion opposed-piston engine
includes a crown part, a skirt part, and an outer part. The crown
part includes a first ring belt region for supporting compression
rings and an end surface shaped to form a combustion chamber with
an end surface of an opposing piston. The skirt part includes a
sidewall and a wristpin bore with a first opening and a second
opening formed in the sidewall. The outer part includes a second
ring belt region for supporting oil control rings. The crown part
is joined to an upper end of the sidewall with one or more welding
seams. The outer part is joined to a lower end of the sidewall with
a welding seam.
Inventors: |
MACKENZIE; RYAN G.; (San
Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ACHATES POWER, INC. |
San Diego |
CA |
US |
|
|
Assignee: |
ACHATES POWER, INC.
San Diego
CA
|
Family ID: |
62002509 |
Appl. No.: |
16/556106 |
Filed: |
August 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2018/025557 |
Mar 30, 2018 |
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16556106 |
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62478932 |
Mar 30, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02F 2200/00 20130101;
F02F 3/0015 20130101; F02F 2003/0061 20130101; F02B 75/282
20130101; F02F 3/003 20130101 |
International
Class: |
F02F 3/00 20060101
F02F003/00; F02B 75/28 20060101 F02B075/28 |
Claims
1. A multi-part piston of a two-stroke cycle, internal combustion
engine comprising: a crown part with a first circumferential ring
belt region; a skirt part with a sidewall including a first end and
a second end; and, an outer part with a second circumferential ring
belt region; wherein the crown part is joined to the first end of
the skirt part by one or more first weld seams and the outer part
is joined to the second end of the skirt part by a second weld
seam.
2. The piston of claim 1, wherein the crown part is made of a first
material and the skirt part is made of a second material.
3. The piston of claim 2, wherein the first material comprises a
metal or metal alloy with a high strength at high temperatures, and
the second material comprises one or more of: 4140 steel, stainless
steel, 10xx carbon steel, ductile iron, austempered ductile iron,
compacted graphite iron, grey iron, any type of SAE graded steel,
titanium, an austenitic nickel-chromium-based superalloy, and a
nickel-based steel alloy.
4. The piston of claim 1, wherein the crown part comprises a forged
metal part and the skirt part comprises a forged metal part.
5. The piston of claim 1, wherein the crown part comprises a forged
metal part and the lower part comprises a forged metal part.
6. The piston of claim 1, wherein the skirt part comprises a forged
metal part and the lower part comprises a forged metal part.
7. A piston of an opposed-piston engine, comprising: a crown part
comprising an end surface including means for forming a combustion
chamber with an end surface of an opposing piston in a cylinder of
an opposed-piston engine, and a circumferentially-extending
compression ring belt region with one or more ring grooves; a skirt
part comprising a first end, a second end, and a wristpin bore with
a wristpin bore axis formed in a sidewall of the skirt part; an
outer part comprising a circumferentially-extending oil ring belt
region with one or more ring grooves; one or more first weld seams
joining the crown part with the first end of the skirt part; and a
second weld seam joining the second end of the skirt part with the
outer part; in which the compression ring belt region is coaxially
aligned with the oil ring belt region along a longitudinal axis of
the piston.
8. The piston of claim 7, wherein the crown part is made of a first
material and the skirt part is made of a second material.
9. The piston of claim 8, wherein the first material comprises a
metal or metal alloy with a high strength at high temperatures, and
the second material comprises one or more of: 4140 steel, stainless
steel, 10xx carbon steel, ductile iron, austempered ductile iron,
compacted graphite iron, grey iron, any type of SAE graded steel,
titanium, an austenitic nickel-chromium-based superalloy, and a
nickel-based steel alloy.
10. The piston of claim 7, wherein the crown part comprises a
forged metal part and the skirt part comprises a forged metal
part.
11. The piston of claim 7, wherein the crown part comprises a
forged metal part and the outer part comprises a forged metal
part.
12. The piston of claim 7, wherein the skirt part comprises a
forged metal part and the outer part comprises a forged metal
part.
13. The piston of claim 7, wherein the crown part comprises a
forged metal base crown including 4140 steel and, the skirt part
comprises a forged metal base skirt including a steel alloy or an
aluminum alloy.
14. The piston of any one of claims 7-13, wherein the means for
forming a combustion chamber includes an axis registered to the
longitudinal wristpin bore axis with a predetermined angle between
the two axes.
15. A method for making a piston of an opposed-piston engine, the
method comprising: providing a crown part comprising a sidewall
with a first ring belt region; providing a skirt part, the skirt
part comprising a wristpin bore having a longitudinal wristpin bore
axis; providing an outer part that comprises a second ring belt
region; welding the crown part and skirt part together; and welding
the outer part and the skirt part together.
16. The method of claim 15, further comprising transforming a piece
of metal using forging to create the crown part, the skirt part,
and/or the outer part of the piston.
17. The method of claim 16, wherein welding the crown part and
skirt part together comprises one or more of friction welding,
shielded active gas welding, shielded metal arc welding, gas
tungsten arc welding, gas metal arc welding, flux-cored arc
welding, submerged arc welding, electroslag welding, and electric
resistance welding.
18. The method of claim 16, wherein welding the crown part and the
outer part together comprises one or more of friction welding,
shielded active gas welding, shielded metal arc welding, gas
tungsten arc welding, gas metal arc welding, flux-cored arc
welding, submerged arc welding, electroslag welding, and electric
resistance welding.
19. The method of claim 16, wherein welding the crown part and
skirt part together comprises induction heating of the crown part
and the skirt part.
20. The method of claim 16, wherein welding the skirt part and the
outer part together comprises induction heating of the skirt part
and the outer part.
21. The method of claim 16, further including forming ring grooves
in the first and second belt regions.
22. The method of any of claims 15-21, wherein the crown part
further comprises an end surface with means for forming a
combustion chamber with an end surface of an opposing piston in a
cylinder of an opposed-piston engine, the combustion chamber
including an axis, and further wherein welding the crown part and
skirt part together comprises orienting the combustion chamber
forming means axis to the longitudinal wristpin bore axis with a
predetermined angle between the two axes.
23. A piston of an opposed-piston engine, comprising: a crown part
comprising an end surface including means for forming a combustion
chamber with an end surface of an opposing piston in a cylinder of
an opposed-piston engine, and a circumferentially-extending
compression ring belt region with one or more ring grooves; a skirt
part comprising a sidewall, a first end, a second end, and a
wristpin bore, formed in the sidewall; an outer part comprising a
circumferentially-extending oil ring belt region with one or more
ring grooves; first weld seams connecting the crown part with the
first end of the skirt part; and a second weld seam connecting the
second end of the skirt part with the outer part; in which the
compression ring belt region is coaxially aligned with the oil ring
belt region along a longitudinal axis of the piston.
24. The piston of claim 23, wherein the crown part further
comprises an undercrown and the skirt part further comprises an
interior wall situated within the sidewall near the first end, in
which the first weld seams include: an inner weld seam between a
radially inner circumferential surface on the interior wall and a
corresponding inner circumferential surface on the undercrown; and,
an inner weld seam between a radially outer circumferential surface
on the interior wall and a corresponding outer circumferential
surface on the undercrown.
25. The piston of claim 24, the sidewall defining a piston
longitudinal axis, wherein the first weld seams are aligned in a
planar cut of the piston which is orthogonal to the piston
longitudinal axis.
26. The piston of claim 23, wherein the crown part and the skirt
part are registered with respect to an axis of the wristpin
bore.
27. A piston of an opposed-piston engine, comprising: a crown part
comprising an end surface including means for forming a combustion
chamber with an end surface of an opposing piston in a cylinder of
an opposed-piston engine, and a circumferentially-extending
compression ring belt region with one or more ring grooves; a skirt
part comprising a sidewall, a first end, a second end, and a
wristpin bore, formed in the sidewall; and, an outer part
comprising a circumferentially-extending oil ring belt region with
one or more ring grooves; in which the crown part is connected to
the first end of the skirt part by one of welding, threading, and
press fitting; and, in which the second end of the skirt part is
connected to the outer part by one of welding, threading, and press
fitting
Description
PRIORITY
[0001] This application is a continuation of PCT application
PCT/US2018/025557, filed Mar. 30, 2018, which claims priority to
U.S. 62/478,932, filed Mar. 30, 2017.
RELATED APPLICATIONS
[0002] This application contains subject matter related to the
subject matter of the following patent applications: U.S. patent
application Ser. No. 13/136,955, filed Aug. 15, 2011, for "Piston
Constructions for Opposed-Piston Engines," now U.S. Pat. No.
9,163,505, issued on Oct. 20, 2015; U.S. patent application Ser.
No. 13/776,656, filed Feb. 25, 2013, for "Rocking Journal Bearings
for Two-Stroke Cycle Engines," now U.S. Pat. No. 9,175,725, issued
on Nov. 3, 2015; U.S. patent application Ser. No. 14/075,926, filed
Nov. 8, 2013, for "Lubricating Configuration For Maintaining
Wristpin Oil Pressure In A Two-Stroke Cycle, Opposed-Piston
Engine," now U.S. Pat. No. 9,038,593, issued on May 26, 2015; U.S.
patent application Ser. No. 14/199,877, filed Mar. 6, 2014, for
"Piston Cooling Configurations Utilizing Lubricating Oil From a
Bearing Reservoir in an Opposed-Piston Engine," now U.S. Pat. No.
9,470,136, issued on Oct. 18, 2016; U.S. patent application Ser.
No. 14/596,855, filed Jan. 14, 2015, for "Piston Cooling for
Opposed-Piston Engines", published as U.S. 2016/0201544, now U.S.
Pat. No. 9,759,119, issued on Sep. 12, 2017; and, U.S. patent
application Ser. No. 15/687,368, filed Aug. 25, 2017, for "Piston
Cooling for Opposed-Piston Engines", published as U.S. 2017/0370273
on Dec. 28, 2017.
FIELD
[0003] The field is piston constructions for internal combustion
engines. More specifically the invention relates to construction of
a piston of an opposed-piston engine, which implements a multi-part
piston configuration having two ring belt regions.
BACKGROUND
[0004] Pistons of opposed-piston internal combustion engines are
constructed differently than conventional pistons that form
combustion chambers against a cylinder head. This is true
particularly for opposed-piston engines in which the movements of
the pistons control the opening and closing of the ports which
allow charge air and exhaust to flow into and out of the engine's
cylinders. As is described in greater detail in some of the related
applications listed above, modifications to the pistons of
opposed-piston engines can be made that allow for piston cooling,
lubrication, and durability while aiming for reduced emissions and
power performance goals.
[0005] In a two-stroke cycle, opposed-piston engine, there is at
least one ported cylinder with a pair of pistons disposed for
counter-moving operation in the cylinder's bore. To-and-fro sliding
motion of the pistons in the cylinder is guided by the bore
surface. In a compression stroke, the pistons approach each other
to form a combustion chamber between their end surfaces in an
intermediate zone of the bore. In a power stroke, the pistons move
apart in response to a combustion event. As the pistons slide
together and apart, sets of inner piston rings installed in the
crowns of the pistons contact the bore surface to seal the
combustion chamber, and sets of outer piston rings installed in the
piston skirts, near outer ends of the skirts, contact the bore
surface to control the transport of lubricating oil into and out of
the cylinder. Piston movement enables the rings to spread
lubricating oil over and across the surface of the bore for the
purpose of reducing friction between the bore surface on one hand
and the rings and skirts of the pistons on the other. Further,
during a compression stroke, when the pistons are near top center
(TC) locations in the cylinder, the outer rings are positioned
between the intake and exhaust ports and the open ends of the
cylinder, providing a seal that keeps crankcase gas, oil mist, and
vapor from mixing with intake air and exhaust gas.
[0006] In some cases, the pistons are provided with a skirt
configuration that presents a minimized contact area with the
cylinder bore surface, which reduces piston/bore friction and
piston mass to the benefit of engine performance and durability.
The configuration is constituted of a narrowing of the skirt's
waist along a wristpin axis, between the sets of inner and outer
piston rings. The configuration widens to
circumferentially-arranged ring belt portions in the crown and base
of the skirt where grooves are formed to support the inner and
outer ring sets, respectively. In other cases, it may be beneficial
to increase the contact area between the piston skirt and the
cylinder bore surface such that the skirt presents an outer surface
that corresponds more completely in shape to the cylinder's bore
surface. In such cases, the configuration of the skirt's outer
surface may have the shape of a cylindrical surface with no
narrowing of the skirt's waist along the cylindrical surface,
between the inner and outer ring sets.
[0007] Each piston may be manufactured from separate parts that
include a crown and a skirt which are joined using conventional
techniques. Typically the crown and skirt parts comprise weldable
materials, such as steel, that are manufactured by casting,
forging, or equivalent processes in which various internal and
external structures are formed. The internal structures include
circumferentially-extending joining surfaces in the crown and skirt
where the parts are connected by means of welding.
[0008] In some aspects, including the skirt configuration with a
minimized contact area, manufacture of the skirt part by forging
may present problems with respect to formation of the second ring
belt for the outer piston rings. If a second ring belt is included
in the forged part, the wall thickness of the skirt must be
substantial enough to meet the radial width requirements of the
ring belt. But, all else being equal, a piston with a thick skirt
wall is more massive than one with a thin skirt wall, which can
adversely affect engine performance and efficiency. Additional
machining of the forged skirt portion to reduce wall thickness adds
cost and time to piston construction that may not be justified in
mass production. Accordingly, there is a need for a piston
construction in a two-stroke opposed-piston engine that affords a
thin skirt wall while supporting an outer ring belt region.
[0009] On the other hand, when it is beneficial to maximize the
contact area between the piston skirt and cylinder bore,
manufacturability may be improved due to elimination of the
transition in wall thickness between the second ring belt and the
skirt. Accordingly, there is a need for a piston construction in a
two-stroke opposed-piston engine that affords a thicker skirt wall
while supporting an outer ring belt region.
SUMMARY
[0010] In either case, a unique construction is realized in a
multi-part piston of a two-stroke cycle, internal combustion engine
in which a crown part has a first circumferential ring belt region,
a skirt part has a sidewall with a first and second ends, and an
outer part has a second circumferential ring belt region, wherein
the crown part is joined to the first end of the skirt part by two
or more first weld seams and the outer part is joined to the second
end of the skirt part by a second weld seam.
[0011] In some implementations, a piston of a two-stroke cycle,
opposed-piston engine is provided in which the piston includes a
crown part and a skirt part with an outer skirt portion. The crown
part includes an end surface with a bowl means shaped for forming a
combustion chamber with the end surface of an opposing piston, and
an annular compression ring belt region. The skirt part includes a
sidewall that defines a piston longitudinal axis, and a wristpin
bore with spaced-apart bore openings formed in the sidewall and
aligned along a longitudinal wristpin bore axis that intersects the
piston axis. Two or more inner weld seams join the crown part and a
first end of the skirt part. The outer skirt portion includes an
annular oil ring belt region. An outer weld seam joins the outer
skirt portion to a second, open end of the sidewall.
[0012] In some implementations, a piston of a two-stroke cycle,
opposed-piston engine is provided in which the piston includes a
crown part and a skirt part with an outer skirt portion. The crown
part includes an end surface with a bowl means shaped for forming a
combustion chamber with the end surface of an opposing piston, and
an annular compression ring belt region. The skirt part includes a
sidewall that defines a piston longitudinal axis, and a wristpin
bore with spaced-apart bore openings formed in the sidewall and
aligned along a longitudinal wristpin bore axis that intersects the
piston axis. Two or more inner weld seams join the crown part and a
first end of the skirt part. The outer skirt portion includes an
annular oil ring belt region. An outer weld seam joins the outer
skirt portion to a second, open end of the sidewall
[0013] In some aspects, the crown part includes a first interior
wall means for defining an upper surface of a circumferential
cooling gallery and the inner portion of the skirt part includes
second interior wall means for defining a lower surface of the
circumferential cooling gallery.
[0014] In some other aspects, the bowl means has an axis extending
between a pair of diametrically-opposed, shaped openings in a
periphery of the end surface that can be oriented to the
longitudinal wristpin bore axis with a predetermined angle between
the two axes.
[0015] Further, in another related aspect, a method for making a
piston for an opposed-piston engine is provided, in which the
method includes providing a crown part, providing a skirt part,
providing an outer part, welding the crown part and skirt part
together, and welding the outer part and the skirt part together.
The provided piston crown part includes a sidewall with a first
ring belt region. The skirt part includes a wristpin bore with a
longitudinal wristpin bore axis. The following may be present in
the method in any suitable combination. Welding the crown part and
skirt part together can include orienting the combustion chamber
forming means axis to the longitudinal wristpin bore axis with a
predetermined angle between the two axes. The method can include
transforming a piece of metal using forging to create the crown
part, the skirt part, and/or the outer part of the piston. Welding
the crown part and skirt part together can include one or more of
friction welding, shielded active gas welding, shielded metal arc
welding, gas tungsten arc welding, gas metal arc welding,
flux-cored welding, submerged arc welding, electroslag welding,
electric resistance welding, magnetic pulse welding, and other
equivalent welding processes. Welding the skirt part and the outer
part together can include one or more of friction welding, shielded
active gas welding, shielded metal arc welding, gas tungsten arc
welding, gas metal arc welding, flux-cored arc welding, submerged
arc welding, electroslag welding, electric resistance welding,
laser beam welding, and electron beam welding. Welding the crown
part and skirt part together can include induction heating of the
crown part and the skirt part. Welding the skirt part and the outer
part together can include induction heating of the skirt part and
the outer part. In the method, the crown part can include an end
surface with bowl means shaped for forming a combustion chamber
with an end surface of an opposing piston in a cylinder of an
opposed-piston engine, and the combustion chamber can include an
injection axis. In such methods, welding the crown part and the
skirt part together can include orienting the combustion chamber
forming means injection axis to the longitudinal wristpin bore axis
with a predetermined angle between the two axes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a schematic drawing of a prior art
opposed-piston engine.
[0017] FIG. 2A is an exploded isometric view of an exemplary
multi-part piston showing separate crown, skirt, and outer parts
that are to be joined together by welding. FIG. 2B is an isometric
view that shows the exemplary multi-part piston assembled for use
in an opposed-piston engine.
[0018] FIG. 3 is a side sectional view of the assembled piston of
FIG. 2B taken along a wristpin bore axis of the piston.
[0019] FIG. 4 is a side sectional view of the assembled piston of
FIG. 2B taken transversely to the wristpin bore axis.
[0020] FIG. 5 is a plan view of a piston crown showing the
orientation of a combustion chamber injection axis with respect to
a wristpin bore axis.
[0021] FIG. 6 shows a method for making a multi-part piston for use
in an opposed-piston engine as described herein.
[0022] FIG. 7A is an exploded isometric view of another exemplary
multi-part piston showing separate crown, skirt, and outer parts
that are to be joined together by welding.
[0023] FIG. 7B is an isometric view that shows the exemplary
multi-part piston assembled for use in an opposed-piston
engine.
[0024] FIG. 8 is a side sectional view of the assembled piston of
FIG. 7B taken along a wristpin bore axis of the piston.
[0025] FIG. 9 is a side sectional view of the assembled piston of
FIG. 7B taken transversely to the wristpin bore axis.
DETAILED DESCRIPTION
[0026] The multi-part piston embodiments described and illustrated
herein are improvements and modifications of piston designs for
two-stroke cycle engines, opposed-piston engines for example. Also
described are methods for fabrication and use of the modified
piston configurations.
[0027] A two-stroke cycle engine is an internal combustion engine
that completes an operating cycle with a single complete rotation
of a crankshaft and two strokes of a piston connected to the
crankshaft. One example of a two-stroke cycle engine is an
opposed-piston engine in which two pistons are disposed in
opposition in the bore of a cylinder. During engine operation,
combustion takes place in a combustion chamber formed in the bore
between the end surfaces of the two pistons when the pistons move
through respective top center locations in the bore. When used
herein, the term "combustion chamber" refers to the minimum volume
within the cylinder that is bounded by the end surfaces of the
pistons and the annular portion of the bore between the end
surfaces during operation of the engine in each cycle of engine
operation.
[0028] As seen in FIG. 1, an opposed-piston engine 1 has at least
one ported cylinder 2. For example, the engine may have one ported
cylinder, two ported cylinders, three ported cylinders, or four or
more ported cylinders. For purposes of illustration, the engine 1
is presumed to have a plurality of ported cylinders. Each cylinder
2 has a bore 12. Exhaust and intake ports 14 and 16 are formed in
respective ends of the cylinder such that the exhaust port 14 is
longitudinally separated from the intake port 16. Each of the
exhaust and intake ports 14 and 16 includes one or more
circumferential arrays of openings. Exhaust and intake pistons 18
and 20 are slidably disposed in the bore 12 with their end surfaces
22 and 24 opposing one another. The exhaust pistons 18 are coupled
to a crankshaft 30, and the intake pistons 20 are coupled to a
crankshaft 32. Each of the pistons is coupled to its associated
crankshaft by a bearing assembly 26 and a connecting rod 28. For
this disclosure, a cylinder may comprise a boring or a formed space
in an engine block, or a liner (or sleeve) retained in a tunnel in
an engine block.
[0029] In the engine shown in FIG. 1, a lubrication system that
supplies oil to lubricate the moving parts of the engine 1 includes
an oil reservoir 44 from which pressurized oil is pumped by a pump
42 to a main gallery 40. The main gallery 40 supplies pressurized
oil to the crankshafts 30 and 32, typically through drillings 36 to
the main bearings (not seen). From grooves in the main bearings,
pressurized oil is provided to grooves in the big end bearings of
the connecting rods 28. From there, pressurized oil flows through
drillings 34 in the connecting rods to the bearings 26. Such a
lubrication system may be present in the engine 1 but should not be
considered to be limiting with respect to the description of the
opposed-piston engine or any of its components.
[0030] The operational cycle of an opposed-piston engine is well
understood. In response to combustion occurring between their end
surfaces 22, 24, the opposed pistons 18 and 20 move away from
respective top center (TC) locations in the cylinder. While moving
from TC, the pistons keep their associated ports closed until they
approach respective bottom center (BC) positions. The pistons may
move in phase so that the exhaust and intake ports 14, 16 open and
close in unison; alternatively, one piston may lead the other in
phase, in which case the intake and exhaust ports have different
opening and closing times. As the pistons move through their BC
locations exhaust products flowing out of the exhaust port 14 are
replaced by charge air flowing into the cylinder through the intake
port 16. After reaching BC, the pistons reverse direction and the
ports are again closed by the pistons. While the pistons continue
moving toward TC, the charge air in the cylinder 2 is compressed
between the end surfaces 22 and 24. Each end surface is shaped for
forming a combustion chamber with the adjacent end surface of the
opposing piston. As the pistons advance to their respective TC
locations in the cylinder bore, fuel is injected directly through
the cylinder sidewall by nozzles 38, into compressed charge air.
The mixture of charge air and fuel is compressed in the combustion
chamber formed between the end surfaces 22 and 24 of the pistons 18
and 20. When the mixture reaches an ignition temperature, the fuel
ignites. Combustion results, driving the pistons apart, toward
their respective BC locations.
[0031] Piston Construction: FIGS. 2A and 2B show a piston 200 for
an opposed-piston engine constructed according to this disclosure.
FIG. 2A shows three separate parts that are joined by welding or an
equivalent process to yield the assembled piston shown in FIG. 2B.
A wristpin is shown in some of these drawings for a clearer
understanding of certain construction features of the piston but is
not intended to limit the scope of this disclosure. A piston 200
with a longitudinal axis 201 comprises a crown part 210, a skirt
part 220 with a piston sidewall 222, and an outer part 223. The
piston 200 is configured so that the skirt part 220 is between the
crown part 210 and the outer 223 part along the piston's
longitudinal axis 201. The crown part 210 and the skirt part 220
are joined by welding circumferentially-extending joining surfaces
of the crown and skirt parts at one end of the sidewall 222. The
outer part 223 and the skirt part are joined by welding
circumferentially-extending joining surfaces of the skirt and outer
parts at an opposite end of the sidewall 222.
[0032] The crown part 210 has an end surface 212 shaped to define a
combustion chamber with the end surface of an opposing piston in
the engine. In the end surface 212, there is a bowl 219 and notches
217 which open into the bowl through the peripheral edge 213 of the
crown part. The notches 217 are shaped to guide entry of fuel into
the combustion chamber. The bowl 219 has a major or longitudinal
axis 214. In this example, the notches 217 are spaced along the
longitudinal axis 214 of the bowl, so as to be situated at
diametrically opposed locations on the peripheral edge 213. The
bowl's axis 214 is collinear with a combustion chamber injection
axis with reference to which fuel is injected. The shape of the end
surface 212 shown in FIGS. 2A and 2B limits the scope of this
disclosure only to the extent that it cooperates with the end
surface of an opposing piston to define a shape of a combustion
chamber in an opposed-piston engine with direct side injection by
at least two injectors. Many other such end surface shapes are
possible; see, for example, and without limitation, the end surface
shapes for pistons of opposed-piston engines that are described and
illustrated in U.S. Pat. No. 8,800,528, US publication
2013/0213342, WO publication 2012/158756, US publication
2014/0014063, US publication 2015/0122227, US publication
2016/0290224, and US publication 2017/0030262.
[0033] With reference to FIGS. 2A, 2B, 3, and 4, a land 221
occupying an external circumferential side surface of the crown
part 210 meets the end surface 212 at the peripheral edge 213. A
first circumferential ring belt region 224 adjoins the land. In
some preferred cases, the piston 200 is assembled before ring
grooves are formed in the belt region 224, as suggested by FIG. 2A.
In other cases, the belt region 224 may be grooved before assembly
of the piston. In any case, when the piston 200 is fully assembled,
the ring belt region 224 comprises a plurality of ring grooves in
which compression rings (not shown) are seated. In some instances,
a ring groove may also be provided in the ring belt region 224 for
an oil control ring. In this specification, the ring belt region
224 is referred to as an "inner ring belt region" because the
piston rings which it supports ride in the innermost regions of a
cylinder bore in a typical opposed-piston application. Because it
supports compression rings which seal against the region of the
cylinder bore surface where the combustion chamber is formed, the
ring belt region 224 may also be termed the "compression ring belt
region". The interior of the crown part 210 includes an undercrown
225. In some aspects, the undercrown 225 includes structures for
defining cooling chambers.
[0034] The piston sidewall 222 is at least partially cylindrical
and extends along the longitudinal axis 201 from a first end 226 to
a second end 227 of the skirt part 220. The second end 227 is open.
An interior wall 228 of the skirt that is centered on the
longitudinal axis 201 is situated within the sidewall 222 near the
first end 226. In some aspects the interior wall 228 includes
support structures for a wristpin and other structures for defining
cooling chambers. Preferably, but not necessarily, the interior
wall 228 on one side defines a portion of a wristpin bore 230 where
a wristpin 231 is received and retained. The wristpin bore 230
includes bore openings 232 formed in bosses 233 in the sidewall.
The bore openings 232 are coaxially aligned along a common wristpin
axis 241. The bosses 233 are formed in recesses 234 on the outer
surface of the sidewall 222. As best seen in FIG. 3, the recesses
234 result in an hourglass-like narrowing of the sidewall 222 along
the wristpin bore axis 241, which reduces friction between the
sidewall and the cylinder bore surface as the piston moves during
engine operation.
[0035] When the crown part 210 and the skirt part 220 are welded
together, a circumferential cooling gallery 243 and a central
cooling chamber 245 are defined between the interior wall 228 of
the skirt part 220 and the undercrown 225. Here it can be seen that
provision of the crown and skirt as separate pieces is a
particularly useful technique of piston construction. It permits
complex interior structures of the piston such as the wristpin bore
230, the cooling gallery 243, and the cooling chamber 245 to be
realized by relatively simple forging or casting of portions of the
structures in the separate undercrown 225 and interior wall 228,
which are then brought together to define the interior structures
when the crown part 210 and skirt part 220 are joined.
[0036] The outer part 223 is an essentially annular piece that
comprises a land 239 occupying an external circumferential side
surface of the outer part 223 that adjoins a second circumferential
ring belt 240 region. In some preferred cases, the piston 200 is
assembled before ring grooves are formed in the ring belt region
240 as suggested by FIG. 2A. In other cases, the ring belt region
240 may be grooved before assembly of the piston. In any case, the
ring belt region 240 has a plurality of ring grooves in which oil
control rings (not shown) are seated when the piston 200 is fully
assembled. In this specification, the ring belt region 240 is
referred to as an "outer ring belt region" because the piston rings
which it supports ride in the outermost regions of a cylinder bore
in a typical opposed-piston application. Because it supports oil
rings which wipe oil from the outer cylinder bore surface in the
outer ends of the cylinder, the ring belt region 240 may also be
termed the "oil ring belt region".
[0037] As shown in FIGS. 2B, 3, and 4, when the outer part 223 and
the skirt part 220 are welded together, the outer ring belt region
240 defines an open outer end of the skirt part 220, and therefore,
of the piston 200. With the piston 200 assembled by welding the
crown part 210, skirt part 220, and outer part 223 together, the
ring belt regions 224 and 240 occupy respective circumferential
ends of the piston 200 that are coaxially aligned with and
separated along the piston axis 201.
[0038] In FIGS. 3 and 4, a line 250 approximates preferred
locations of first weld seams between the crown part 210 and the
skirt part 220. The crown part 210 and the skirt part 220 can be
joined (or, "connected") by one or more circumferential weld seams
at circumferentially-extending joining surfaces in the vicinity of
the line 250. In the example shown, there is an inner weld seam
250a between a radially inner circumferential surface 251 (best
seen in FIG. 2A) on a circular rib extending from the interior wall
228 and a corresponding inner circumferential surface 252 on the
undercrown 225. In the example shown, there is another inner weld
seam 250b between a radially outer circumferential surface 253
(best seen in FIG. 2A) on a circular rib extending from the
interior wall 228 and a corresponding outer circumferential surface
254 on the undercrown 225. Preferably, but not necessarily, the
first weld seams 250a and 250b are aligned in a cut plane
containing the line 250 which is orthogonal to the piston
longitudinal axis 201 and are formed in the same welding step.
However, other weld seam alignments and orientations are
contemplated. Many techniques of welding crown and skirt parts
using circumferential weld seams to form internal cooling galleries
and cooling chambers are known. See, for example, U.S. Pat. No.
8,327,537 in this regard.
[0039] As seen in FIG. 3, near the second end 227 of the skirt part
220, on the interior surface of the sidewall 222 there are
undercuts 260 that result from formation of the bosses 233 in the
narrowed portion 234 of the sidewall 222. The narrowed portion 234
widens to the annular sections in the crown part 210 and the outer
part 223 where grooves are formed in the inner and outer ring belt
regions 224 and 240, respectively. The undercuts 260 would make it
difficult to fabricate the skirt part 220 and the outer part 223 as
a single, forged part. However, the undercuts 260 can be formed by
manufacturing the skirt part 220 and the outer part 223 separately,
by forging for example, with portions of the undercuts 260 formed
in the two parts 220 and 223, and then welding the two parts 220
and 223 together along corresponding circumferentially-extending
joining surfaces. In addition to simplifying the fabrication of the
skirt part with the wristpin bore and the narrowed skirt portion
234, other advantages are gained.
[0040] In a first advantage, the outer part 223 can be manufactured
as an annular piece, with circumferentially uniform symmetry, which
eliminates a step of registration between the skirt part 220 and
the outer part 223 when joined by welding.
[0041] A second advantage can be seen in FIG. 4, wherein the
sidewall 222 can be made with a relatively thin radial width
W.sub.1 in the non-narrowed portions of the skirt 222 by means of a
forging step for example, so as to reduce the mass of the piston
200. In this regard the radial width W.sub.1 of the sidewall 222 in
the non-narrowed portion is less than the radial width W.sub.2 of
the second ring belt region 240.
[0042] With reference to FIGS. 3 and 4, the skirt part 220 and the
outer part 223 are joined (or, "connected") by a second weld seam
270. The weld seam 270 is formed between a
circumferentially-extending free end 272 of the skirt part 220 and
a circumferentially-extending free end 274 of the outer part 223
(best seen in FIG. 2B). The free ends 272 and 274 have respective
circumferentially-extending joining surfaces which are positioned
in alignment and welded together, preferably by means of a friction
welding process, although this is not intended to be limiting.
[0043] In some aspects, which may be appreciated with respect to
FIGS. 2A and 2B, the crown part 210 may have to be registered (or,
"clocked") with respect to the skirt part 220 in preparation for
making the first weld seams. For example, the crown part 210 may
have to be positioned with respect to the skirt part 220 such that
there is a predetermined orientation between the combustion chamber
axis 214 and the wristpin bore axis 241 when the two parts are
welded. In this instance, the diametrically-opposed notches 217,
which are aligned along the axis 214, will have a particular
orientation to the wristpin bore 230 and thus to the skirt part
220, which may be critical to the placement of fuel injectors in a
cylinder block of an opposed-piston engine, depending on size and
weight requirements. With reference to FIG. 5, the angle O between
the combustion chamber injection axis 214 and the wristpin bore
axis 241 can be between 30 degrees and 90 degrees. In some
implementations, the angle O between the axes can be between 30 and
35 degrees; the angle O between the bowl axis 214 and the
longitudinal wristpin bore axis 241 can be 32 degrees.
Alternatively, depending on the configuration of other components
in the engine, the angle O between the axes can be between 45 and
55 degrees; the angle O can be 58 degrees.
[0044] The piston 200 shown in FIGS. 2A, 2B, 3, and 4 may be
fabricated from three or more forged parts that are finished, or
partially finished, then joined (e.g., welded) as per FIGS. 3 and
4. The materials and methods of construction of the piston 200 may
be conventional for medium and/or heavy duty use or for large bore
applications. For example, the crown part 210 and the skirt part
220 may be formed separately of compatible materials (e.g., forged
steel crown, cast iron skirt part) and joined by welding or
brazing. Other materials can include laminated structures, hybrid
structures, composite structures, and the like, including thermal
barrier coatings, ceramic-metal composites (e.g., cermets),
high-temperature metal alloys, laser ablated/structured surfaces,
and the like.
[0045] In a piston for use in an opposed-piston engine, the crown
part can include a forged metal base crown, with a shape including
the bowl, undercrown and other features that can be nearly finished
in dimension. Coatings may be applied to the surfaces of the forged
base parts (i.e., the base crown part, the base skirt part, the
base outer part). The coatings can be a thermal barrier coating, an
oxidation prevention coating, an oil retention coating, and the
like. Forged base parts can be designed to facilitate the forging
process and to require little to no (i.e. minimal) machining and
finishing after forging. The aforementioned coatings can be applied
to the crown part, the skirt part, and the outer part either before
or after welding these parts are together.
[0046] Forging metal parts, particularly steels, requires design
considerations, known in the metal-working arts. Some of these
design considerations include draft, or taper, in side walls and
interior filets. Forged parts will also have distinct changes in
the grain or crystal structure of the metal, and often times
forging is used to impart strength characteristics to forged pieces
that may not be present in machined or cast metal pieces.
[0047] The piston constructions described herein above can be
combined with selection of materials that can allow for easier
fabrication, lower costs, and/or lower weight without much, if any,
sacrifice in piston performance. In some implementations, the crown
part of a piston can include a metal or metal alloy that has high
strength at high temperature. Additionally, or alternatively, the
skirt and outer parts of a piston can include conventional piston
materials. Materials that can be used in fabrication of the piston
include: investment cast 4140 steel, stainless steel, investment
cast 10xx carbon steel, sand cast steel, sand cast ductile iron,
austempered ductile iron, sand cast compacted graphite iron, sand
cast grey iron, any type of SAE graded steel, titanium, an Inconel
alloy, a Hastelloy.RTM. alloy, or a combination thereof.
[0048] In implementations where the crown part of a piston is made
of a different material than the skirt and outer parts, or where
manufacturing can be simplified by fabricating the piston in
multiple segments, one or more joining techniques can be used to
assemble the piston. A welding technique used to join parts of a
piston together per FIGS. 3 and 4 may include any of friction
welding, shielded active gas welding, shielded metal arc welding,
gas tungsten arc welding, gas metal arc welding, flux-cored arc
welding, submerged arc welding, electroslag welding, and/or
electric resistance welding. Additionally, or alternatively,
induction heating of two parts to be joined can be used along with
precise positioning of the two parts, particularly where precise
relative positioning impacts the functioning of the opposed-piston
engine, such as when the piston end surface has asymmetric
features.
Material Example 1
[0049] Presume that a three-part piston is designed for an
opposed-piston engine in which the end surface will experience peak
cylinder pressures in excess of 200 bar. In order to achieve a
durable, high strength construction, the crown part may be a forged
piece comprising 4140 steel, the skirt part may be a forged piece
comprising 4140 steel, and the outer part may be cut from tube
stock comprising a weldable, wear resistant steel and machined to
obtain the desired features. In some cases it may be desirable to
forge the outer part from a piece comprising a weldable, wear
resistant steel material.
Material Example 2
[0050] Presume that a three-part piston is designed for an
opposed-piston engine in which the end surface will experience peak
cylinder pressures less than or equal to 200 bar. In order to
achieve a durable construction of appropriate strength, the crown
part may be a forged piece comprising a microalloyed steel, the
skirt part may be a forged piece comprising a microalloyed steel,
and the outer part may be cut from tube stock comprising a
weldable, wear resistant steel and machined to obtain the desired
features. In some cases it may be desirable to forge the outer part
from a piece comprising a weldable, wear resistant steel
material.
[0051] Manufacture:
[0052] FIG. 6 shows a method 600 for making a piston for use in an
opposed-piston engine as described herein. The method includes
providing a crown part for a piston, as in 605. As described above,
the crown part may be of a first material while the balance of the
piston is of a second material, or two or more different materials.
The crown part provided includes a first ring belt region (e.g.,
for accommodating compression ring grooves) and an end surface with
a combustion forming means (e.g., a bowl). Preferably, the crown
part is forged, followed by machining as required on a weld face of
the undercrown.
[0053] A skirt part that includes a wristpin bore is provided in
the method, as in 610. The material used to fabricate the crown
part may be the same or different from that used to fabricate the
skirt part. Preferably, the skirt part is forged, followed by
machining as required on a weld face of the interior wall that will
be joined to the weld face of the undercrown and on a weld face of
the open end that will be joined to a weld face of the outer
part.
[0054] Further, the method includes providing an outer part that
includes a second ring belt region (e.g., for accommodating oil
control ring grooves), as in 615. The outer part can be of the same
material of the skirt part and/or of the crown part. Alternatively,
the outer part can include a different material, a material that is
not used in any other part of the piston. Preferably, the outer
part is cut from tube stock comprising a weldable, wear resistant
steel and machined to obtain the weld face that will be joined to
the weld face at the open end of the skirt part.
[0055] The method includes welding the crown part to the skirt
part, as in 620. In some instances, the crown part and the skirt
part are registered with one another and then the crown part is
welded to the skirt part. Preferably inner and outer weld seams are
made to join the crown part and skirt part as seen in FIGS. 3 and 4
by means of one hybrid Induction weld operation.
[0056] Then, the skirt part is joined to the outer part by welding,
as in 625. Welding can include induction heating and physical
joining, as well as friction welding or electron beam welding.
Further, the welding process (i.e., physical joining process) can
involve a heat-treatment after welding to relieve stresses and/or
heal cracks caused by the physically joining portions of the piston
together. Preferably, the single weld seam is made to join skirt
part and the outer part as seen in FIGS. 3 and 4 by means of an
inertia friction welding operation.
[0057] Preferably, a final processing step 630 may include
heat-treatment following the physical joining processes to allow
for formation of desired materials phases and mixtures,
particularly along the weld seams. Preferably, the processing step
630 includes machining the inner and outer ring bands to form ring
grooves as required by design considerations. Additionally, the
final processing step may include machining the skirt to form the
wristpin bore openings.
[0058] Second Piston Construction:
[0059] There may be instances where certain aspects of the piston
200 (FIGS. 2A and 2B) limit its applicability. For example, the
recesses 234 in the sidewall 222 where the bosses 233 are located
may pose challenges related to manufacturability, durability, and
operation of the piston in heavy duty applications. In these and
other applications, it may be desirable to have a piston with
somewhat more mass and symmetry, and a greater
sidewall-to-cylinder-bore contact area, than the piston 200. For
such instances, FIGS. 7A and 7B show another piston 700 for an
opposed-piston engine constructed according to this disclosure.
FIG. 7A shows three separate parts that are joined by welding to
yield the assembled piston shown in FIG. 7B. A wristpin is shown in
some of these drawings for a clearer understanding of certain
construction features of the piston but is not intended to limit
the scope of this disclosure. A piston 700 has a longitudinal axis
701, a crown part 710, a skirt part 720 with a piston sidewall 722,
and an outer part 723. The piston 700 is configured so that the
skirt part 720 is between the crown part 710 and the outer 723 part
along the piston's longitudinal axis 701. The crown part 710 and
the skirt part 720 are joined by welding
circumferentially-extending joining surfaces of the crown and skirt
parts at one end of the sidewall 722. The outer part 723 and the
skirt part 720 are joined by welding circumferentially-extending
joining surfaces of the skirt and outer parts at an opposite end of
the sidewall 722.
[0060] The crown part 710 has an end surface 712 shaped to define a
combustion chamber with the end surface of an opposing piston in
the engine. In the end surface 712, there is a bowl 719 and notches
717 which open into the bowl through the peripheral edge 713 of the
crown part. The notches 717 are shaped to guide entry of fuel into
the combustion chamber. The bowl 719 has a major or longitudinal
axis 714. In this example, the notches 717 are spaced along the
longitudinal axis 714 of the bowl, so as to be situated at
diametrically opposed locations on the peripheral edge 713. The
bowl's axis 714 is collinear with a combustion chamber injection
axis with reference to which fuel is injected. The shape of the end
surface 712 shown in FIGS. 7A and 7B limits the scope of this
disclosure only to the extent that it cooperates with the end
surface of an opposing piston to define a shape of a combustion
chamber in an opposed-piston engine with direct side injection by
at least two injectors. Many other such end surface shapes are
possible; see, for example, and without limitation, the end surface
shapes for pistons of opposed-piston engines that are described and
illustrated in the above-referenced US patents and
publications.
[0061] With reference to FIGS. 7A, 7B, 8, and 9, a land 721
occupying an external circumferential side surface of the crown
part 710 meets the end surface 712 at the peripheral edge 713. A
first circumferential ring belt region 724 formed on the side
surface of the crown part adjoins the land. In some preferred
cases, the piston 700 is assembled before ring grooves are formed
in the belt region 724, as suggested by FIG. 7A. In other cases,
the belt region 724 may be grooved before assembly of the piston.
In any case, when the piston 700 is fully assembled, the ring belt
region 724 has a plurality of ring grooves in which compression
rings (not shown) are seated. In some instances a ring groove may
also be provided in the ring belt region 724 for an oil control
ring. In this specification, the ring belt region 724 is referred
to as an "inner ring belt region" because the piston rings which it
supports ride in the innermost regions of a cylinder bore in a
typical opposed-piston application. Because it supports compression
rings which seal against the region of the cylinder bore surface
where the combustion chamber is formed, the ring belt region 724
may also be termed the "compression ring belt region". The interior
of the crown part 710 includes an undercrown 725. In some aspects,
the undercrown 725 includes structures for defining cooling
chambers.
[0062] The piston sidewall 722 is substantially cylindrical and
extends along the longitudinal axis 701 from a first end 726 to a
second end 727 of the skirt part 720. The second end 727 is open.
An interior wall 728 of the skirt that is centered on the
longitudinal axis 701 is situated within the sidewall 722 near the
first end 726. In some aspects, the interior wall 728 includes
support structures for a wristpin and other structures for defining
cooling chambers. Preferably, but not necessarily, the interior
wall 728 on one side defines a portion of a wristpin bore 730 where
a wristpin 731 is received and retained. The wristpin bore 730
includes bore openings 732 formed in bosses 733 defined in the
sidewall 722. The bosses 733 and bore openings 732 are coaxially
aligned along a common wristpin axis 741. The openings 732 open
through the sidewall 722 and are configured to receive a wristpin
731. As in FIGS. 7A, 7B, 8, and 9, the sidewall 722 presents a
substantially cylindrical surface, without the narrowed waist
portions 223 of the piston 200. In this regard, a "substantially
cylindrical surface" means approximating a cylindrical surface, but
not necessarily exactly cylindrical. For example, some degree of
ovality may be provided in the overall shape of the sidewall and/or
other portions of the piston.
[0063] When the crown part 710 and the skirt part 720 are welded
together, a circumferential cooling gallery 743 and a central
cooling chamber 745 are defined between the interior wall 728 of
the skirt part 720 and the undercrown 725. Here it can be seen that
provision of the crown and skirt as separate pieces is a
particularly useful technique of piston construction. It permits
complex interior structures of the piston such as the wristpin bore
730, the cooling gallery 743, and the cooling chamber 745 to be
realized by relatively simple forging or casting of portions of the
structures in the separate undercrown 725 and interior wall 728,
which are then brought together to define the interior structures
when the crown part 710 and skirt part 720 are joined.
[0064] The outer part 723 is an annular piece that comprises a land
739 occupying an external circumferential side surface of the outer
part 723 that adjoins a second circumferential ring belt 740
region. In some preferred cases, the piston 700 is assembled before
ring grooves are formed in the ring belt region 740 as suggested by
FIG. 7A. In other cases, the ring belt region 740 may be grooved
before assembly of the piston. In any case, the ring belt region
740 has a plurality of ring grooves in which oil control rings (not
shown) are seated when the piston 700 is fully assembled. In this
specification, the ring belt region 740 is referred to as an "outer
ring belt region" because the piston rings which it supports ride
in the outermost regions of a cylinder bore in a typical
opposed-piston application. Because it supports oil rings which
wipe oil from the outer cylinder bore surface in the outer ends of
the cylinder, the ring belt region 740 may also be termed the "oil
ring belt region".
[0065] As shown in FIGS. 7B, 8, and 9, when the outer part 723 and
the skirt part 720 are welded together, the outer ring belt region
740 defines an open outer end of the skirt part 720, and therefore,
of the piston 700. With the piston 700 assembled by welding the
crown part 710, skirt part 720, and outer part 723 together, the
ring belt regions 724 and 740 occupy respective circumferential
ends of the piston 700 that are coaxially aligned along the piston
axis 701.
[0066] In FIGS. 8 and 9, a line 750 approximates preferred
locations of first weld seams between the crown part 710 and the
skirt part 720. The crown part 710 and the skirt part 720 can be
joined (or, "connected") by one or more circumferential weld seams
at circumferentially-extending joining surfaces in the vicinity of
the line 750. In the example shown, there is an inner weld seam
750a between a radially inner circumferential surface 751 (best
seen in FIG. 7A) on a circular rib extending from the interior wall
728 and a corresponding radially inner circumferential surface 752
on the undercrown 725. In the example shown, there is another inner
weld seam 750b between a radially outer circumferential surface 753
(best seen in FIG. 7A) on a circular rib extending from the
interior wall 728 and a corresponding radially outer
circumferential surface 754 on the undercrown 725. Preferably, but
not necessarily, the first weld seams 750a and 750b are aligned in
a cut plane containing the line 750 which is orthogonal to the
piston longitudinal axis 701 and are formed in the same welding
step. However, other weld seam alignments and orientations are
contemplated. Many techniques of welding crown and skirt parts
using circumferential weld seams to form internal cooling galleries
and cooling chambers are known. See, for example, U.S. Pat. No.
8,327,537 in this regard.
[0067] As seen in FIG. 8, near the second end 727 of the skirt part
720, on the interior surface of the sidewall 722 there are
undercuts 760 that result from formation of the bosses 733 in the
sidewall 722. The undercuts 760 can be formed by manufacturing the
skirt part 720 and the outer part 723 separately, by forging for
example, with the undercuts 760 formed in the skirt part 720 near
the second end 727, and then welding the two parts 720 and 723
together by means of a second weld seam. For example, the skirt
part 720 and the outer part 723 can be joined by a second weld seam
770a at circumferentially-extending joining surfaces in the
vicinity of the line 770. In the example shown, the weld seam 770a
is formed between a circumferential surface 771 (best seen in FIG.
7A) on the outer part 723 and a corresponding circumferential
surface 772 on the skirt part 720 at the open end 727.
[0068] In some aspects, the crown part 710 and the skirt part 720
may have to be registered in preparation for being joined by first
weld seams, as explained above with respect to FIG. 5. In other
aspects, the parts 710, 720, and 723 may be fabricated and joined
together by welding as described above with respect to the piston
200.
[0069] Alternate Joining Features:
[0070] In the preceding embodiments, the crown part, skirt part,
and outer part are described as being joined or connected by
welding. There may be instances wherein it may be rational and
useful to connect or join the parts by purely mechanical methods
and means, including threading, press fitting, and so on. It may
also be the case where the three parts are joined or connected by
some combination of welding, threading, and press fitting.
[0071] Those skilled in the art will appreciate that the specific
embodiments set forth in this specification are merely illustrative
and that various modifications are possible and may be made therein
without departing from the scope of the subject multi-part piston
construction for an opposed-piston engine.
* * * * *