U.S. patent application number 16/790552 was filed with the patent office on 2020-06-18 for piston assembly with opposing injection regions 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 | 20200191090 16/790552 |
Document ID | / |
Family ID | 63684521 |
Filed Date | 2020-06-18 |
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United States Patent
Application |
20200191090 |
Kind Code |
A1 |
MACKENZIE; RYAN G. |
June 18, 2020 |
PISTON ASSEMBLY WITH OPPOSING INJECTION REGIONS FOR AN
OPPOSED-PISTON ENGINE
Abstract
A piston for an opposed-piston, internal combustion engine
includes a crown with an end surface having a bowl shaped to form a
combustion chamber with an end surface of an opposing piston in the
opposed-piston engine. A substantially circumferential top land of
the crown meets the end surface at a substantially circular
peripheral edge, and a skirt comprising a sidewall extends from a
substantially circumferential belt region of the crown. A wristpin
bore with a wristpin axis opens through the sidewall. The end
surface of the piston includes a pair of injection regions across
which fuel is injected into the bowl. The injection regions are
disposed in substantially diametrically-opposed quadrants of the
end surface which are defined by the wristpin axis and a connecting
rod envelope axis substantially orthogonal to the wristpin axis.
Each injection region extends along a respective arc concentric
with the substantially circular peripheral edge.
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: |
63684521 |
Appl. No.: |
16/790552 |
Filed: |
February 13, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2018/049214 |
Aug 31, 2018 |
|
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16790552 |
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62555201 |
Sep 7, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02F 3/003 20130101;
F02F 2003/0061 20130101; F02F 3/26 20130101; F05C 2201/0448
20130101; F02F 3/22 20130101; F02B 23/0663 20130101; F02F 2200/04
20130101; F02B 23/0678 20130101; F02B 75/282 20130101; F02B 23/0618
20130101; F02F 3/0023 20130101; B23P 15/10 20130101 |
International
Class: |
F02F 3/22 20060101
F02F003/22; F02F 3/00 20060101 F02F003/00 |
Claims
1. A piston for an opposed-piston engine, comprising: a crown with
an end surface comprising a bowl configured to form a combustion
chamber in cooperation with an adjacent end surface of an opposing
piston; a substantially circumferential top land of the crown which
meets the end surface at a substantially circular peripheral edge;
a skirt comprising a sidewall extending away from the crown; a
wristpin bore that opens through the sidewall, the wristpin bore
having a wristpin bore axis; the wristpin bore configured to
receive a wristpin that couples the piston to a connecting rod that
swings in an envelope of motion defined by an envelope axis, the
envelope axis being substantially orthogonal to the wristpin bore
axis; and, the end surface including a pair of injection regions
across which fuel is injected into the bowl; in which the injection
regions are disposed in respective diametrically-opposed quadrants
of the end surface, the diametrically-opposed quadrants being
defined by the wristpin bore axis and the envelope axis; and, in
which each injection region extends along a respective arc
concentric with the substantially circular peripheral edge.
2. The piston of claim 1, the wristpin bore comprising a first
opening formed in a first pin boss in the sidewall and a second
opening formed in a second pin boss in the sidewall, the openings
being coaxially aligned along the wristpin bore axis.
3. The piston of claim 1, the end surface further comprising a pair
of injection trenches, each injection trench being formed in a
respective injection region and extending from the substantially
circular peripheral edge to the bowl.
4. The piston of claim 3, in which the injection trenches are
situated in diametrically opposed locations.
5. The piston of claim 1, the end surface further comprising two
diametrically-opposed injection trenches, each injection trench
being formed in a respective injection region and being shaped for
guiding a spray of injected fuel into the bowl.
6. The piston of claim 1, the crown further comprising an interior
annular cooling gallery defined at least partially by an inner
surface of the substantially circumferential top land, and inlet
passageways positioned in the interior annular cooling gallery
substantially in alignment with the injection trenches.
7. The piston of claim 6, the wristpin bore comprising a first
opening formed in a first pin boss in the sidewall and a second
opening formed in a second pin boss in the sidewall, the openings
being coaxially aligned along the wristpin bore axis.
8. The piston of claim 6, the end surface further comprising two
diametrically-opposed injection trenches, each injection trench
being formed in a respective injection region and being shaped for
guiding a spray of injected fuel into the bowl.
9. The piston of claim 8, in which the injection trenches are
situated in diametrically opposed locations.
10. The piston of claim 6, in which the arcuate extent of each
injection region subtends an angle of about 50-70 degrees with the
vertex of the angle being at the center of the substantially
circular peripheral edge.
11. The piston of claim 1, in which the arcuate extent of each
injection region subtends an angle of about 50-70 degrees with the
vertex of the angle being at the center of the substantially
circular peripheral edge.
12. A piston assembly for an opposed-piston engine, comprising: a
crown with an end surface comprising a bowl configured to form a
combustion chamber in cooperation with an adjacent end surface of
an opposing piston; a substantially circumferential top land of the
crown which meets the end surface at a substantially circular
peripheral edge; a skirt comprising a sidewall extending away from
the crown; a wristpin bore in the sidewall; a wristpin with a
wristpin axis received in the wristpin bore; a connecting rod
coupled to the wristpin for swinging in an envelope of motion
defined by an envelope axis, the envelope axis being substantially
orthogonal to the wristpin axis; a pair of injection trenches in
the end surface at the substantially circular peripheral edge
through which fuel is injected into the bowl; and, the injection
trenches being situated in respective diametrically-opposed
quadrants of the end surface defined by the wristpin axis and the
envelope axis.
13. The piston assembly of claim 12, the wristpin bore comprising a
first opening formed in a first pin boss in the sidewall and a
second opening formed in a second pin boss in the sidewall, the
openings being coaxially aligned along the wristpin axis.
14. The piston assembly of claim 12, each injection trench
extending from the substantially circular peripheral edge to the
bowl.
15. The piston assembly of claim 14, in which the injection
trenches are situated in diametrically opposed locations of the end
surface.
16. The piston assembly of claim 12, each injection trench being
shaped for guiding a spray of injected fuel into the bowl.
17. The piston assembly of claim 12, the crown further comprising
an interior annular cooling gallery defined at least partially by
an inner surface of the substantially circumferential top land
region and inlet passageways positioned in the interior annular
cooling gallery substantially in alignment with the injection
trenches.
18. The piston assembly of claim 17, the wristpin bore comprising a
first opening formed in a first pin boss in the sidewall and a
second opening formed in a second pin boss in the sidewall, the
openings being coaxially aligned along the wristpin axis.
19. The piston assembly of claim 18, each injection trench
extending from the substantially circular peripheral edge to the
bowl.
20. The piston assembly of claim 19, in which the injection
trenches are situated in diametrically opposed locations of the end
surface.
21. The piston assembly of claim 12, in which the injection
trenches are positioned along respective arcuate portions of the
substantially circular peripheral edge, each arcuate portion
spanning about 70.degree. and being substantially centered in one
of the diametrically-opposed quadrants.
22. An opposed-piston engine, comprising: a cylinder block with a
plurality of cylinders disposed in an inline array along a length
of the cylinder block; a pair of pistons disposed in opposition in
each cylinder; each piston comprising a wristpin with a wristpin
axis, the wristpin coupling the piston to a connecting rod that
swings in a connecting rod motion envelope having an envelope axis
that is substantially orthogonal to the wristpin axis, the piston
further comprising a crown with an end surface and a bowl in the
end surface configured to form a combustion chamber in cooperation
with a bowl of an adjacent end surface of an opposing piston, the
end surface including a pair of injection regions across which fuel
is injected into the bowl; in which the injection regions are
disposed in respective diametrically-opposed quadrants of the end
surface, the diametrically-opposed quadrants being defined by the
wristpin axis and the envelope axis; and, in which each injection
region extends along a respective arc concentric with the
substantially circular peripheral edge.
23. The engine of claim 22, the wristpin bore comprising a first
opening formed in a first pin boss in the sidewall and a second
opening formed in a second pin boss in the sidewall, the openings
being coaxially aligned along the wristpin axis.
24. The engine of claim 22, the end surface further comprising a
pair of injection trenches, each injection trench being formed in a
respective injection region and extending from the substantially
circular peripheral edge to the bowl.
25. The engine of claim 24, in which the injection trenches are
situated in diametrically opposed locations.
26. The engine of claim 22, the end surface further comprising two
diametrically opposed injection trenches, each injection trench
being formed in a respective injection region and being shaped for
guiding a spray of injected fuel into the bowl.
27. The engine of claim 22, the crown further comprising an
interior annular cooling gallery defined at least partially by an
inner surface of a substantially circumferential top land of the
crown, inlet passageways positioned in the interior annular cooling
gallery in alignment with the injection regions.
28. The engine of claim 27, the wristpin bore comprising a first
opening formed in a first pin boss in the sidewall and a second
opening formed in a second pin boss in the sidewall, the openings
being coaxially aligned along the wristpin axis.
29. The engine of claim 27, the end surface further comprising a
pair of injection trenches, each injection trench being formed in a
respective injection region and extending from the substantially
circular peripheral edge to the bowl.
30. The engine of claim 29, in which the injection trenches are
situated in diametrically opposed locations.
31. The engine of claim 27, the end surface further comprising two
diametrically opposed injection trenches, each injection trench
being formed in a respective injection region and being shaped for
guiding a spray of injected fuel into the bowl.
32. The engine of claim 22, in which the arcuate extent of each
injection region subtends an angle of about 50-70 degrees with the
vertex of the angle being at the center of the substantially
circular peripheral edge.
Description
PRIORITY AND RELATED APPLICATIONS
[0001] This application is a continuation of International Patent
Application PCT/US2018/049214, "Piston Assembly With Opposing
Injection Regions for an Opposed-Piston Engine, filed Aug. 31,
2018, which claims priority to U.S. Provisional Application
62/555,201, "Piston Assembly With Opposing Injection Regions for an
Opposed-Piston Engine", filed Sep. 7, 2017. This application
contains subject matter related to the subject matter of the 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 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; and
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.
FIELD OF THE INVENTION
[0002] The present invention is directed to a piston with a unique
end surface construction which makes it particularly suited for use
in an opposed-piston internal combustion engine with direct side
injection of fuel.
[0003] More specifically, the piston has a construction with an end
surface configuration in which injection regions have a unique
orientation with respect to wristpin and connecting rod features of
the piston, which enables stationary oil jets to provide coolant
for piston thermal management from positions favorable for
achieving a compact engine configuration.
[0004] The present invention also relates to a piston construction
with a unique location of diametrically-opposed injection regions
on the end surface which permits fuel injectors to be positioned
more favorably in an opposed-piston engine.
BACKGROUND OF THE INVENTION
[0005] The related '725 patent describes a piston construction
designed for an opposed-piston engine which includes a wristpin
support structure mounted within the interior of the piston skirt.
An upper portion of the wristpin support structure provides a wall
for an interior annular cooling gallery. Inlet openings in the wall
permit streams of liquid coolant enter the annular coolant gallery.
The annular cooling gallery achieves an optimal cooling effect when
the streams of coolant are aligned with injection trenches on the
piston end surface by which fuel emitted through
diametrically-opposed fuel injectors enters a combustion chamber.
However, the features necessary for attachment of the wristpin
bearing support structure to the interior of the skirt greatly
restrict design options for placement of stationary oil jets that
deliver the streams of coolant to the annular cooling gallery.
Furthermore, the restrictions on oil jet placement result in a
cascade of additional design restrictions regarding other elements
including injection trenches and fuel injectors that limit progress
toward realization of good piston thermal management in a compact
opposed-piston engine.
[0006] Replacement of the separate wristpin support structure with
a wristpin bore formed integrally with the piston skirt eliminates
the attachment features that restrict placement of stationary oil
jets and fuel injectors, thereby enabling a unique piston
construction for an opposed-piston with direct side injection that
permits stationary oil jets and fuel injectors to be positioned
more favorably in an opposed-piston engine.
SUMMARY OF THE INVENTION
[0007] In an aspect of the invention, a piston for an
opposed-piston engine is provided having a crown with an end
surface in which a bowl is configured to form a combustion chamber
in cooperation with an adjacent end surface of an opposing piston.
A substantially circumferential top land of the crown meets the end
surface at a substantially circular peripheral edge, and a skirt
comprising a sidewall extends axially away from the substantially
circumferential top land. A wristpin bore with a wristpin bore axis
is formed in the sidewall. The wristpin bore is provided for
receiving a wristpin that couples the piston to a connecting rod
that swings in an envelope of motion defined by an envelope axis
which is substantially orthogonal to the wristpin bore axis. The
end surface of the piston includes a pair of injection regions
across which fuel is injected into the bowl. The injection regions
are disposed in substantially diametrically-opposed quadrants of
the end surface which are defined by the wristpin bore axis and the
envelope axis. Each injection region extends along a respective arc
concentric with the substantially circular peripheral edge. In some
cases, the arcuate extent of each injection region may subtend an
angle of about 50-70 degrees with the vertex of the angle being at
the center of the substantially circular peripheral edge.
[0008] Preferably, the wristpin bore has a first opening formed in
a first pin boss in a first wall portion of the sidewall and a
second opening formed in a second pin boss in a second wall portion
of the sidewall, and the openings are coaxially aligned along the
wristpin bore axis.
[0009] In some aspects, an injection trench is formed in each
injection region and injection trench extends from the
substantially circular peripheral edge to the bowl.
[0010] In other aspects, the end surface has two diametrically
opposed injection trenches, each injection trench being formed in a
respective injection region and being shaped for guiding a spray of
injected fuel into the bowl.
[0011] In another aspect of the invention, an opposed-piston engine
has a cylinder block with a plurality of cylinders disposed in an
inline array along a length of the cylinder block. A pair of
pistons is disposed in opposition in each cylinder. Each piston has
a wristpin with a wristpin axis, which couples the piston to a
connecting rod that swings in a connecting rod motion envelope
having an envelope axis. The envelope axis is substantially
orthogonal to the wristpin axis. The piston has a crown with an end
surface and a bowl in the end surface configured to form a
combustion chamber in cooperation with a bowl of an adjacent end
surface of an opposing piston. The end surface includes a pair of
injection regions across which fuel is injected into the bowl. The
injection regions are disposed in respective diametrically-opposed
quadrants of the end surface that are defined by the wristpin axis
and the envelope axis. Each injection region extends along a
respective arc concentric with the substantially circular
peripheral edge.
[0012] These features of the invention result in advantages that
will be readily understood when the following detailed description
of the invention is considered in conjunction with the
below-described drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic drawing showing an opposed-piston
engine, and is properly labeled "Prior Art."
[0014] FIG. 2 is a side view, in perspective, of a
piston/connecting rod assembly for a two-stroke cycle,
opposed-piston engine, and is properly labeled "Prior Art."
[0015] FIG. 3 is an exploded view of a bearing support structure of
the piston shown in FIG. 2, and is properly labeled "Prior
Art."
[0016] FIG. 4 is a partially schematic sectional view, in
elevation, of the piston of FIGS. 2 and 3 in a cylinder block of an
opposed-piston engine, and is properly labeled "Prior Art."
[0017] FIG. 5 is an isometric view of a piston constructed for use
in an opposed-piston engine according to the invention.
[0018] FIGS. 6A and 6B are side sectional views of the piston of
FIG. 5, without a wristpin installed in a wristpin bore, taken
along orthogonal central planes that pass through a skirt of the
piston. FIG. 6C is a side sectional view of the piston of FIG. 5
that corresponds to the view seen in FIG. 6A, with a wristpin
installed in the wristpin bore.
[0019] FIG. 7 is a schematic figure showing the end surface of the
piston of FIG. 5 in plan, without end surface features.
[0020] FIG. 8 is a schematic figure showing the end surface of the
piston of FIG. 5 in plan, with end surface features according to
the invention.
[0021] FIG. 8A is a side sectional view of the piston of FIG. 5
taken along a central plane passing through opposing injector
trenches to show alignment of oil jet inlet passageways with the
injector trenches.
[0022] FIG. 9 is a partially schematic view through a medial cut
plane of an opposed-piston engine having a cylinder block in which
the cylinders are equipped with pistons according to the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0023] Opposed-Piston Engine:
[0024] By way of background, an opposed-piston engine is an
internal combustion 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 during each cycle of engine
operation.
[0025] As seen in FIG. 1, an opposed-piston engine 10 has at least
one ported cylinder 12. 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 10
is presumed to have a plurality of ported cylinders. Each cylinder
12 has a bore 13. Exhaust and intake ports 14 and 16 are formed
near 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 13 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 wristpin 26 and a connecting rod 28. For this
disclosure, a cylinder may comprise a boring or a formed space in a
cylinder block, or a liner (or sleeve) retained in a tunnel in a
cylinder block.
[0026] In the engine 10, a lubrication system that supplies oil to
lubricate moving parts of the engine 10 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 and/or passageways 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 passageways formed in the connecting rods 28 to the
wristpins 26.
[0027] The pistons 18 and 20 are cooled by provision of streams of
oil emitted by stationary oil jets 46 that are mounted in the
engine near respective ends of the cylinder 12. Each oil jet 46
comprises a nozzle aimed through an open end of the cylinder 12 at
an inlet passage of the annular cooling gallery of the piston.
[0028] In some aspects, which are not intended to be limiting, the
engine 10 is equipped with an air management system 50 that may
include one or more of a turbocharger 52, a supercharger 54, and an
EGR channel 56.
[0029] The operational cycle of an opposed-piston engine according
to FIG. 1 is well understood. In response to combustion occurring
between their end surfaces 22, 24, the opposed pistons 18, 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 12 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 directly
injected through one or more openings 38 in the sidewall of the
cylinder 12 into the charge air (this process is called "direct
side injection"), and 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 compression
causes the mixture to reach an ignition temperature, the fuel
ignites. Combustion results, driving the pistons apart, toward
their respective BC locations.
[0030] Piston Constructions:
[0031] A piston for an opposed-piston engine (an "opposed piston")
is constructed differently from a conventional piston that forms a
combustion chamber against the cylinder head of an engine where
valve-controlled intake and exhaust ports are located. In
opposed-piston engines the pistons move together in a ported
cylinder to form a combustion chamber between their end surfaces.
In addition, the movements of the opposed pistons control the
opening and closing of the cylinder ports to allow charge air to
flow into and exhaust to flow out of the engine's cylinders.
[0032] In the first instance, the end surface of a conventional
piston typically includes a bowl shaped to enable the mixing of
charge air with a spray of fuel injected along the axis of the
cylinder in which the piston moves. Such a bowl has a shape that is
symmetric with respect to the piston's axis. In contrast, the end
surface of an opposed piston has a bowl whose features must
accommodate fuel injection in a radial or tangential direction of
the cylinder, typically from a pair of diametrically opposed fuel
injectors. Such a bowl is not symmetric with respect to the
piston's axis.
[0033] In the second instance, a conventional piston supports one
ring band region and a wristpin. However, in addition to these
features, an opposed piston must support a second ring band region
near an open end of the piston in order to scrape excess oil from
the cylinder bore and maintain the seal of an intake port or an
exhaust port when the piston moves through top center. The second
ring band necessitates a longer piston skirt for an opposed piston
than for a conventional piston.
[0034] A third feature which characterizes an opposed piston is a
linkage assembly including a wristpin bearing support that allows
for the interaction of a connecting rod, a wristpin, and the piston
in an environment where the wristpin undergoes continuous
compressive loading throughout the operational cycle of the engine.
U.S. Pat. No. 9,470,136 describes and illustrates a piston bearing
assembly in an opposed-piston engine wherein a biaxial
wristpin/bearing interface induces periodic separation of axially
distributed bearing segments to permit lubricant to reach the
opposing external surfaces of the wristpin and the bearing. The
wristpin is supported in a generally cubic structure which is
installed in the interior of the piston, where the structure is
completely enclosed in the piston skirt.
[0035] The wristpin support structure is separate from the cylinder
skirt, and so the exterior of the skirt is free of bosses and
wristpin bores such that it presents a continuous cylindrical
aspect to the cylinder bore, thereby providing a highly effective
seal between the combustion chamber and crankcase when outfitted
with nothing more than two sets of piston rings. However, the price
paid is a complex and costly construction which necessitates
multiple assembly steps and adds weight to the piston. Further,
although the continuous cylindrical aspect of the skirt enables an
effective seal between the combustion chamber and the crankcase, it
also results in generation of friction in the interface between the
skirt and the cylinder bore.
[0036] FIG. 2 is a perspective view of a prior art piston assembly
for an opposed-piston engine. The piston 100 has a crown 103, and a
skirt with a generally tubular sidewall 105. An end surface 107 of
the crown has a bowl 108 configured to form a combustion chamber in
cooperation with the end surface bowl of an opposing piston.
Opposing injection trenches are provided for guiding fuel emitted
by fuel injectors into the bowl. One such injection trench 109 is
visible in the figure. An inner ring belt region 110 is provided in
a circumferential side surface of the crown for seating compression
rings and oil control rings. An outer ring belt region 112 is
provided in the skirt's sidewall for seating oil scraper rings. A
connecting rod 120 has a big end 122 for coupling to a crank throw
of a crankshaft (not seen) and a small end (not seen) which is
positioned in the interior space defined by the sidewall 105. An
oil groove 124 is formed in the bearing surface of the large end
122. A drilled oil delivery passage (not seen) extends
longitudinally in the connecting rod 120 from the oil groove 124 to
the small end of the connecting rod. Elongate longitudinal slots
125 are formed in opposite sides of the shaft 126 of the connecting
rod between the big end and small end to accommodate stationary oil
jets (not shown) as the connecting rod swings with a pendulum-like
motion during engine operation.
[0037] With reference to FIGS. 3 and 4, the piston 100 includes a
wristpin bearing assembly 200 fixed to the crown undersurface and
disposed in space encircled by the skirt 105. As shown in FIG. 3, a
wristpin support structure includes an upper support member 230 and
a lower support member 240. The upper support member 230 includes a
bearing surface 220 that receives a wristpin 210 mounted to the
small end 127 of the connecting rod 120 by threaded fasteners 211.
The upper and lower support members 230 and 240 are joined around
the wristpin 210 and secured to the crown undersurface by four
fasteners 202 (three of which are visible in FIG. 3) that are
threadably seated in interior bosses (not seen) formed in the crown
undersurface. As seen in FIG. 3, an opening 242 in the lower
bearing support member 240 receives the connecting rod 120. When
assembled, the wristpin support structure retains the wristpin 210
for oscillation on the bearing surface 220 caused by pendulum-like
oscillation of the connecting rod 120 in the opening 242. Similar
single-unit wristpin bearing structures are shown in U.S. Pat. Nos.
9,038,593 and 9,175,725.
[0038] FIG. 4 shows the wristpin bearing assembly 200 installed in
the piston 100 with the piston disposed in the bore of a cylinder
261 of a prior art opposed-piston engine. When assembled in the
manner shown, the upper support member 230 provides a bottom wall
of an interior annular cooling gallery 265. As shown in FIGS. 3 and
4, the upper support member 230 includes inlet passageways 267 with
inlet openings 269 in the bottom wall of the interior annular
cooling gallery 265. As per FIG. 4, stationary oil jets 270 are
positioned to direct streams of oil 272 to the inlet passageways
267 through which the streams enter into the annular cooling
gallery 265. In some instances, a stationary oil jet may be in
substantial alignment with an inlet passageway, as is shown in the
figure; in other instances, the stream of oil emitted by a
stationary jet may be deflected to an inlet passageway. It is
undesirable to place the inlet passageways 267 in alignment with
the axis of the wristpin 210 because the stationary oil jets 270
would require provision of engine space between cylinders, thereby
increasing inter-cylinder spacing and engine length. The inlet
passageways 267 cannot be placed in the locations occupied by the
fasteners 202 shown in FIG. 3. Consequently, the optimal locations
available for the inlet passageways 267 in the wristpin assembly
200 shown on FIGS. 3 and 4 are the diametrically-opposed portions
of the upper support member that are aligned orthogonally to the
wristpin 210. However even these locations have drawbacks. For
example, clearance between the cylinder sidewall 271 and the sides
of cylinder block 274 must be provided for placement of the
stationary oil jets 270, which places a lower limit on a width of
the engine. Further, the stationary oil jets 270 protrude into the
pie-slice-shaped envelope of motion 273 through which the
connecting rod 120 travels. Clearance between the connecting rod
120 and the stationary oil jets 270 is obtained by forming the
elongate longitudinal slots 125 in the shaft of the connecting rod
120, which weakens the connecting rod 120 and increases its cost of
manufacture. The same drawbacks are evident in similar single-piece
wristpin bearing structures that are shown in U.S. Pat. Nos.
9,038,593 and 9,175,725.
[0039] Elimination of the Wristpin Support Structure:
[0040] A construction for a simpler, lighter piston for an
opposed-piston engine eliminates the internal wristpin support
structure of the prior art. FIGS. 5, 6A, and 6B illustrate an
example of a piston 300 for an opposed-piston engine without the
construction limitations associated with wristpin assemblies such
as are shown in FIGS. 3 and 4. The piston 300 has a longitudinal
axis 302, a crown 310 with an end surface 311, and a skirt 320
attached to or formed integrally with the crown. The crown 310 has
a cylindrical sidewall comprising a substantially circumferential
land 312 (called the "top land" because of its proximity to the end
surface 311) that meets the end surface 311 at a substantially
circular peripheral edge 313 which is centered on the longitudinal
axis 302. A substantially circumferential inner ring belt region
314 on the crown extends away from the land 312 in the direction of
the skirt 320. The skirt 320 comprises a sidewall 322 that extends
away from the crown 310 to an open outer end 321 of the skirt. The
end surface 311 is shaped to form a combustion chamber with an
adjacent end surface of an opposing piston in an opposed-piston
engine. The shape of the end surface 311 includes a bowl 316 that
is configured to define the combustion chamber, not with a cylinder
head, but with a bowl in the end surface of the opposing piston.
The shape shown in FIG. 5 of the end surface 311 limits the scope
of the invention only to the extent that it cooperates with the end
surface of an opposing piston to form a combustion chamber in an
opposed-piston engine. It is possible, but not necessary that the
end surfaces will have identical shapes. Many such end surface
shapes are possible; see, for example, the piston end surface
constructions 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.
[0041] An outer ring belt region 323 is formed in a circumferential
portion 325 of the sidewall 322 near the outer end 321 of the
piston. The sidewall 322 is formed with two opposing curved
sidewall portions 327 separated from one another by two opposing
box wall portions 328. The curved sidewall portions 327 extend away
from the crown 310 toward the open end 321. Relative to the
longitudinal axis 302, the curved sidewall portions 327 may have
the same radius as the crown 310 and the circumferential portion
325 of the sidewall. In other instances, the curved sidewall
portions may have shapes and dimensions adapted for accommodating
thrust differentials experienced during engine operation. The box
wall portions 328 are inset from the curved sidewall portions 327
and run longitudinally in portions of the sidewall 322 between the
inner ring belt region 314 and the outer ring belt region 323. The
box wall portions 328 have wristpin bosses 333 in which
diametrically-opposed, laterally-spaced wristpin bore openings 335
are formed at respective ends of a wristpin bore 336. The wristpin
bore openings 335 are coaxially aligned along a wristpin bore axis
337. A particular piston bearing embodiment will now be described,
although this embodiment is presented for the purpose of
illustration only. Other bearing constructions are contemplated,
although all will utilize the laterally-spaced wristpin bore
openings 335.
[0042] With reference to FIGS. 6A, 6B, and 6C the piston 300
includes an interior wall 340 that defines a portion of the
wristpin bore 336 where a wristpin 350 with a wristpin axis 352 is
received and retained. One side of the interior wall 340 extends
between the wristpin bore openings 335. In the example shown, a
bearing sleeve 354 is received and seated in a recessed portion 341
of the one side. Together, the sleeve 354 and the wristpin bore
openings 335 define the wristpin bore 336 of this example. As per
FIGS. 6A, 6B, and 6C, an interior annular cooling gallery 342 is
defined at least partially by an inner surface of the substantially
circumferential top land 312. The interior wall 340 also functions
as the bottom wall of an interior annular cooling gallery 342 which
is situated in the crown 310 to enable cooling of the land 312 and
the inner ring region 314 during engine operation.
[0043] FIG. 6C shows a piston assembly in which the wristpin 350 is
installed in the wristpin bore of the piston 300. The wristpin 350
has two ends 350e that are received and supported in the wristpin
bore openings 335. The wristpin 350 has a journal surface that
rotates against an opposing surface of the bearing sleeve 354 and
the two ends 350e. The wristpin 350 is attached to the small end
359 of a connecting rod 360 by threaded fasteners 362, which
configures the piston for installation in an opposed-piston engine
in the manner shown in FIG. 1 in which the large end 361 of the
connecting rod would be coupled to a crankpin of a crankshaft. The
wristpin 350 is secured against lateral movement in the wristpin
bore by disc-shaped caps 363 retained in the bosses 333 by standard
features such as grooves, press fitting, and so on.
[0044] Opposing Injection Regions:
[0045] The piston construction thus far described eliminates any
need for the wristpin support structure of the prior art piston of
FIGS. 2-4. With this improvement, restrictions on placement of
elements that deliver coolant and fuel to the piston are
significantly relaxed. The beneficial results may be understood
with reference to FIGS. 7-9.
[0046] FIG. 7 is a schematic diagram in which the end surface 311
on the crown 310 of the piston 300 is seen in plan, without surface
features, together with a motion envelope 400 representing the
moving 360.degree. circular path that the big end 361 (FIG. 6C) of
the connecting rod travels as the piston 300 reciprocates between
TC and BC locations during engine operation. The outer edges 405
and 406 of the motion envelope 400 represent the extreme positions
reached by the outer edges of the big end 361 when the piston 300
is midway between TC and BC on successive strokes of engine
operation. The envelope of motion 400 may be defined by an envelope
axis 410, the envelope axis 410 being substantially orthogonal to
the wristpin axis 352, when the wristpin 350 and the connecting rod
360 are assembled to the piston as shown in FIG. 6C; without the
wristpin 350 and connecting rod 360 coupled to the piston (FIGS. 6A
and 6B), the same relationship is given by the wristpin bore axis
337, and a diameter of the substantially circular peripheral edge
313 that is orthogonal to the wristpin bore axis 337.
[0047] The usual prior art locations of the inlet passageways as
constrained by the prior art wrist pin support structure shown in
FIGS. 3 and 4 are indicated in FIG. 7 by reference numerals 267.
However since there is no separate wristpin support structure to
attach to the interior of the piston 300 shown in FIGS. 5 and
6A-6C, inlet passageways are not limited to being situated at
diametrically-opposed locations that are aligned orthogonally to
the wristpin 350 (as is illustrated by the case with the prior art
arrangements exemplified by FIG. 4). Instead, inlet passageways are
free to be situated at locations that are offset arcuately between
the wristpin 350 and the envelope of motion 400, with the result
that unique piston configurations are made possible. These
locations are indicated by the shaded areas labeled "Additional
Space for Placement of Inlet Passageways" in FIG. 7.
[0048] FIG. 8 shows the end surface 311 of the crown 310 with the
substantially circular peripheral edge 313, the bowl 316, and the
longitudinal axis 302 of the piston visible. The interior annular
cooling gallery 342 is indicated by dashed lines. A conventional
2-dimensional grid is superimposed on the end surface for the
purpose of illustrating aspects of the invention. The 2-dimensional
grid has a first axis 420 and a second axis 422 that is orthogonal
to the first axis 420. If the piston 300 is not fully assembled (as
seen in FIGS. 6A and 6B) one of the axes 420, 422 corresponds to
the wristpin bore axis 337 and the other of the axes 420, 422 is a
diameter of the substantially circular peripheral edge 313 if the
piston 300; otherwise, if the piston is fully assembled as shown in
FIG. 6C, one of the axes corresponds to the wristpin axis 352 and
the other axis corresponds to the envelope axis 410. The orthogonal
axes 420 and 422 define four quadrants of the end surface 311. For
illustration, these quadrants may be denoted as I, II, III, and IV,
in the usual fashion. The end surface 311 includes a pair of
injection regions 430 and 432 across which fuel is directly
injected by fuel injectors (which are not shown) into a combustion
chamber formed at least partially by the bowl 316. Inlet
passageways 433 for admission of streams of oil into the interior
annular cooling gallery 342 are situated in the interior wall 340
substantially in alignment with the injection regions 430 and
432.
[0049] The injection regions 430 and 432 are disposed in respective
diametrically-opposed quadrants of the end surface 311. The figure
shows the injection regions 430 and 432 disposed in quadrants I and
III, but this is not meant to be limiting as they may alternatively
be in quadrants II and IV, together with the inlet passageways 433.
Each one of the injection regions 430 and 432 extends along a
respective arcuate section of the substantially circular peripheral
edge 313 and is concentric with the substantially circular
peripheral edge. The injection regions 430 and 432 may or may not
be aligned in diametric opposition. Preferably, the arcuate extent
of each of the injection regions 430 and 432 subtends an angle
.alpha. of about 50-70 degrees with the vertex of the angle being
at the center of the substantially circular peripheral edge, which
is coincident with the longitudinal axis 302.
[0050] As per FIG. 8, in most cases injection trenches 435 are
formed in the crown 310 in peripheral portions of the end surface
311 to accommodate fuel injection from fuel injector nozzles into
the bowl 316. Each injection trench 435 is situated in a respective
one of the injection regions 430 and 432. Each injection trench
extends from the substantially circular peripheral edge 313 to the
bowl 316. The injection trenches 435 have shapes that guide fuel
sprays emitted by fuel injectors in predetermined directions into
turbulent charge air in a combustion chamber formed in part by the
bowl 316. Preferably the end surface 311 has a pair of injection
trenches 435. FIG. 8 shows two injection trenches 435 aligned
substantially in diametric opposition across the bowl 316. However
this is not intended to be limiting. There may be cases in which
the injection regions have no trenches, but may be contoured in
some manner to accommodate a particular fuel spray pattern. For
example an injection region may have a smoothly-curved, somewhat
shallow depression formed to accommodate a particular fuel spray
pattern. Further, the relative positioning of the trenches may
deviate from diametric opposition according to design
considerations regarding engine construction and combustion
performance.
[0051] The shapes of injection trenches often present edges and
other surface irregularities where hot spots occur in the piston
end surface during combustion. Hot spots lead to asymmetrical
thermal stress, wear, and possibly piston crown fracture. Even in
cases where the surface contour is less emphatic, such as without
trenches, the injection regions may endure a higher thermal load
than end surface regions closer to the interior of the bowl. In any
event, it is desirable to provide directed cooling to the portions
of the crown undersurface that are beneath the injection regions.
Thus, in the example shown in FIGS. 8 and 8A, the inlet passageways
433 are in substantial circumferential alignment with the trenches
435, thereby positioned to guide respective streams of oil emitted
by stationary jets into the annular cooling gallery 342, where the
streams may impinge on surface portions of the annular cooling
gallery which are nearest the trenches 435. Impinging oil streams
can provide a relatively high heat transfer characteristic to the
regions of the crown where hot spots related to the injection
regions occur.
[0052] The materials and methods of construction of the piston 300
may be conventional for light, medium and/or heavy duty use or for
large bore applications. For example, the crown and skirt part may
be formed separately of compatible and/or complementary materials
(e.g., forged steel crown, cast iron skirt part) and joined by
welding or brazing. Additionally, or alternatively, forming
technology including printing technology can be used to form some
or all of the piston 300 and its components. 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, and
laser ablated/structured surfaces.
[0053] Engine Application.
[0054] FIG. 9 shows an engine configuration made possible by the
unique piston construction shown in FIGS. 5-6C. FIG. 9 is a
partially schematic view taken through a medial cut plane of an
opposed-piston engine having a cylinder block 500 with a plurality
of cylinders 502 disposed in an inline array along a length of the
cylinder block. Although half of each cylinder and only one piston
per cylinder is seen, the craftsman of ordinary skill will
appreciate that a pair of pistons is disposed in opposition in each
cylinder 502. Each piston 504 comprises a piston assembly
constructed according to FIGS. 6C and 8, which includes a wristpin
506 with a wristpin axis which couples the piston to a connecting
rod 510 that swings in a connecting rod motion envelope having an
envelope axis that is substantially orthogonal to the wristpin
axis. Each piston 504 of each pair of pistons has a crown with an
end surface and a bowl 518 in the end surface configured to form a
combustion chamber in cooperation with the bowl of the opposing
piston. The end surface includes a pair of injection regions 520
across which fuel is injected into the bowl. The injection regions
520 are disposed in respective diametrically-opposed quadrants of
the end surface that are defined by the wristpin axis and the
envelope axis as per FIG. 8. As illustrated in FIG. 8, each
injection region extends along a respective arc concentric with the
substantially circular peripheral edge of the crown. This
configuration allows for compact construction of the engine because
the stationary oil jets can be moved inwardly of the side walls of
the crankcases, and fuel injectors 522 may be mounted obliquely
with respect to the length of the cylinder block, thereby yielding
a more compact engine profile. Further, this configuration allows
for a simplified and strengthened construction of the connecting
rods 510 which no longer have to accommodate the stationary oil
jets.
[0055] Those skilled in the art will appreciate that the specific
embodiments set forth in this specification are merely illustrative
of the invention and that various modifications are possible and
may be made thereto without departing from the scope of the
invention.
* * * * *