U.S. patent number RE34,139 [Application Number 07/762,203] was granted by the patent office on 1992-12-08 for engine piston assembly and forged piston member therefor having a cooling recess.
This patent grant is currently assigned to Caterpillar Inc.. Invention is credited to Bruce C. Cooper, Kenton L. Erickson, James A. Green, David S. Nycz.
United States Patent |
RE34,139 |
Cooper , et al. |
December 8, 1992 |
Engine piston assembly and forged piston member therefor having a
cooling recess
Abstract
Present day diesel engines having aluminum piston assemblies are
limited to combustion chamber pressures of approximately 12,410 kPa
(1,800 psi) whereas the desire is to increase such pressures up to
the 15,170 kPa (2,200 psi) range. To reach such levels the instant
piston assembly includes a steel piston member having an upper
cylindrical portion defining a top surface, a depending tubular
wall and an annular cooling recess having one or more machined
surfaces of revolution about a central axis. The cooling recess is
located beneath the top surface and juxtaposed to the top ring
groove for removing heat away therefrom in use. The piston member
is preferably forged and subsequently machined to precisely
controllable dimensions. Moreover, the piston assembly is
preferably of the articulated type and includes a forged aluminum
piston skirt connected to the piston member through a common wrist
pin.
Inventors: |
Cooper; Bruce C. (Chillicothe,
IL), Erickson; Kenton L. (Dunlap, IL), Green; James
A. (Peoria, IL), Nycz; David S. (Peoria, IL) |
Assignee: |
Caterpillar Inc. (Peoria,
IL)
|
Family
ID: |
22994294 |
Appl.
No.: |
07/762,203 |
Filed: |
September 19, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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261663 |
Oct 21, 1988 |
|
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Reissue of: |
291429 |
Dec 23, 1988 |
04867119 |
Sep 19, 1989 |
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Current U.S.
Class: |
123/193.6;
123/41.35; 92/234; 92/239 |
Current CPC
Class: |
F02F
3/0069 (20130101); F02F 3/22 (20130101); F02B
3/06 (20130101); F02F 2003/0061 (20130101); F02F
2200/04 (20130101); F05C 2201/021 (20130101); F05C
2201/0433 (20130101); F05C 2201/0448 (20130101); F05C
2251/042 (20130101) |
Current International
Class: |
F02F
3/16 (20060101); F02F 3/16 (20060101); F02F
3/22 (20060101); F02F 3/22 (20060101); F02F
3/00 (20060101); F02F 3/00 (20060101); F02B
3/00 (20060101); F02B 3/00 (20060101); F02B
3/06 (20060101); F02B 3/06 (20060101); F02F
003/00 () |
Field of
Search: |
;123/193P,41.35,254,41.36 ;92/239,159,6,189,190,208 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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51212185 |
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Dec 1985 |
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AU |
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0106935 |
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May 1984 |
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EP |
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2717084 |
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Mar 1985 |
|
DE |
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3425228 |
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Feb 1986 |
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DE |
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3643039 |
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Jun 1988 |
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DE |
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54-47937 |
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Apr 1979 |
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JP |
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60-187346 |
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Dec 1985 |
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JP |
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554918 |
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Jul 1943 |
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GB |
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Other References
Technical Paper; Mahle Symposium (pp. 3; 77-89) dated May, 1973, by
H. G. Braendel. .
Technical Paper; Associated Engrg. Group Technical Symposium, Paper
No. 7 Title: "Oil Cooled & Electron Beam Welded Pistons for
Diesel Engs." dated 1978, by Dr. R. Monro, et al. .
Technical Paper No. 780781; Society of Automotive Engineers, dated
Sep. 11-14, 1978, by M. D. Roehrle. .
Technical paper No. 770031; Society of Automotive Engineers, dated
Feb. 28-Mar. 4, 1977, by M. D. Roehrle. .
Application filed simultaneously herewith by: B. Ballheimer et al.,
for: Piston Assembly and Piston Member Thereof having a
Predetermined Compression Height to Diameter Ratio. .
Application filed simultaneously herewith by: Robert L. Weber et
al., for: Engine Piston Assembly and Piston Member Therefor Having
A High Top Ring Groove. .
Application filed simultaneously herewith by: Marshall (NMI) Adams
et al., for: A Method Of Producing A Crown For An Articulated
Piston..
|
Primary Examiner: Makay; Albert J.
Assistant Examiner: Macy; M.
Attorney, Agent or Firm: Sterne, Kessler, Goldstein &
Fox
Parent Case Text
This is a continuation-.Iadd.in-part .Iaddend.of Ser. No.
07/261,663, filed Oct. 21, 1988, now abandoned.
Claims
What is claimed:
1. .[.A.THETA. .Iadd.An articulated piston assembly comprising an
upper .Iaddend.forged .Iadd.one piece .Iaddend.steel piston
member.Iadd., a lower aluminum skirt member, and a pin articulately
mounting the members .Iaddend.for reciprocating movement in an
engine.Iadd., the upper piston member .Iaddend.comprising:
an upper portion of substantially cylindrical shape and having a
central axis, a top surface, a tubular wall depending from the top
surface and .Iadd.forged integral with the upper portion, the
tubular wall .Iaddend.having a peripheral groove .Iadd.having a
bottom surface and .Iaddend.adapted to receive a sealing
ring.Iadd., the peripheral groove being spaced a preselected
minimal elevational distance TRH from the top surface.Iaddend., a
lower end surface, and an inwardly facing wall surface extending
upwardly from the lower end surface;
the upper portion further including an outwardly facing wall
surface spaced radially inwardly from the inwardly facing wall
surface and a downwardly facing transition portion blendingly
associated with the inwardly and outwardly facing wall surfaces to
collectively define an annular cooling recess, the transition
portion being .[.elevational.]. .Iadd.elevationally .Iaddend.spaced
a relatively short distance "E" from the top surface.Iadd., the top
of the cooling recess being in juxtaposed elevational relation with
the peripheral groove to provide for removing heat from around the
peripheral groove.Iaddend.; and
the inwardly facing wall surface being a machined surface of
revolution about the central axis .[.integral or one piece
forging.]. .Iadd.to maintain dimensional control and concentricity
between the bottom surface of the peripheral groove and the
inwardly facing wall surface.Iaddend..
2. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the
outwardly facing wall surface and the downwardly facing transition
portion are machined surfaces of revolution about the central
axis.
3. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 1 .Iadd.wherein the
upper piston member .Iaddend.further .[.including.]. includes a
lower portion having a pair of depending pin bosses blendingly
associated with the cooling recess and individually defining a
bore, and the bores being aligned along a common axis.
4. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 3 wherein the upper
portion and lower portion are an integral or one-piece forging.
5. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 4 wherein the
material used for the .[.forging.]. .Iadd.upper piston member
.Iaddend.is a chromium-molybdenum steel.
6. The forged steel piston member of claim 1 wherein the
elevational distance "E" between the top surface and the top of the
cooling recess is approximately 6 mm.
7. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the upper
portion defines a recessed crown surface which contains machined
surfaces of revolution about the central axis so that a relatively
uniform web is defined between the crown surface and the cooling
recess.
8. The .[.forged steel.]. .Iadd.articulated .Iaddend.piston
.[.member.]. .Iadd.assembly .Iaddend.of claim 1 wherein the minimum
radial thickness between the cooling recess and the innermost
portion of the peripheral groove is about 1.74 mm.
9. The piston .Iadd.assembly .Iaddend.of claim 7 wherein the upper
and lower portions are an integrally formed forging.
10. The piston assembly of claim 7 including an aluminum piston
skirt, and a wrist pin connecting the piston member to the piston
skirt.
11. The piston assembly of claim 10 wherein the outwardly facing
wall surface and the downwardly facing transition portion are
machined surfaces of revolution about the central axis.
12. An .[.engine.]. .Iadd.articulated .Iaddend.piston assembly for
an engine of the type having a block defining a bore, a cylinder
liner supported in the block and defining a piston bore, and a
cylinder head connected to the block, wherein the improvement
comprises:
a forged steel .Iadd.piston .Iaddend.member .[.piston.]. having an
upper portion of substantially cylindrical shape and having a
central axis, a peripheral top surface, a tubular wall depending
from the top surface and defining an outwardly facing top land, a
top ring groove .Iadd.spaced .Iaddend.a preselected minimal
elevational distance TRH .Iadd.of about 5 mm .Iaddend.from the top
surface, a lower end surface, and an annular inwardly facing wall
surface extending upwardly from the lower end surface;
the upper portion further including an annular outwardly facing
wall surface spaced radially inward from the inwardly facing wall
surface and a downwardly facing transition portion blendingly
associated with the inwardly and outwardly facing wall surfaces to
collectively define an annular cooling recess located in juxtaposed
relation with to the top ring groove, the inwardly facing wall
surface being a machined surface of revolution about the central
axis; .[.and.].
a lower portion including a pair of depending pin bosses blendingly
associated with the cooling recess and individually defining a bore
and with the bores being aligned on a common axis;
.Iadd.a piston skirt defining a pair of wrist pin receiving bores
aligned with the bores of the pin bosses; and
a wrist pin in the aligned bores for articulately connecting the
piston skirt and the piston member.Iaddend..
Description
TECHNICAL FIELD
This invention relates generally to a compact engine piston
assembly for a high output internal combustion engine, and more
particularly to a steel piston member capable of resisting
relatively high combustion chamber pressures and temperatures and
having machined surfaces of revolution.
BACKGROUND ART
The last several years has seen an increasing amount of emphasis on
designing engines having improved fuel economy and efficiency,
reduced emissions, a greater service life, and an increased power
output per cylinder. The trend has resulted in increasingly more
severe mechanical and thermal requirements on the piston members.
The crown region of a piston member is heated by the burning fuel
and air mixture. The piston assembly including the piston rings
must make effective contact with the cylinder bore to prevent the
egress of hot combustion gases and to control lubricating oil under
all operating conditions. The temperature and combustion pressures
on the piston member particularly must remain within prescribed
material, structural and thermal limits or early failure will
result.
The cooled composite piston assembly disclosed in U.S. Pat. No.
4,581,983 issued to H. Moebus on Apr. 15, 1986 is illustrative of
one configuration that can withstand such increased power output
levels. However, the upper and lower parts thereof are joined
together by welding, and this is a costly process that is
preferably to be avoided.
A more desirable type of piston assembly is disclosed in U.S. Pat.
No. 4,056,044 issued to Kenneth R. Kamman on Nov. 1, 1977. The
Kamman patent, which is assigned to the Assignee of the present
invention, teaches the use of an articulated piston assembly having
an upper piston member and a lower skirt which are individually
pivotally connected to a common wrist pin. Oil directed to a trough
in the skirt is advantageously splashed in a turbulent "cocktail
shaker" action against a recess in the underside of the crown
surface adjacent the ring grooves for cooling the interior of the
piston. Subsequent extensive testing thereof with cast elements has
indicated that the practical level of knowledge on casting
procedures is insufficient to resist combustion pressures above
about 13,790 kPa (2,000 psi). Specifically, an excessive number of
the upper cast steel piston members had so much porosity that
premature failure resulted. On the other hand, a few cast steel
piston members were manufactured with relatively low levels of
porosity so that they survived a relatively rigorous testing
program. While extensive studies were conducted to minimize
porosity levels in the cast members, the levels remain too high.
One way to check for porosity is to fully x-ray piston, which not
only is unacceptable from a cost stand point but also does not
guarantee that the piston is totally free of porosity.
In addition to porosity considerations, it should be appreciated
that the structural shape and strength of each element of an
articulated piston assembly is in a continual stage of being
modified to better resist higher compressive loads and thermally
induced forces. For example, Society of Automotive Engineers, Inc.
Paper No. 770031 authored by M. D. Roehrie, entitled "Pistons for
High Output Diesel Engines", and presented circa Feb. 28, 1977, is
indicative of the great number of laboratory tests conducted
throughout the world on the individual elements. That paper also
discusses a number of considerations to minimize cracking problems
in light alloy or aluminum piston members resulting primarily from
thermal constraints.
U.S. Pat. No. 4,662,047 issued to Rutger Berchem on May 5, 1987
discloses a one-piece piston produced by die pressing of a
previously forged blank to bend an annular cylindrical collar
thereon. A forged piston can offer the capability of resisting high
combustion chamber pressures and temperatures; however, the forging
of parts with relatively thin wall sections having extremely close
dimensional tolerances and the forming of narrow and deep cavities
having precise relative locations is very difficult, if not
impossible. Therefore it is frequently the manufacturing tolerances
that limit or prevent the forging of the thin wall sections and
narrow deep cavities that are so desperately required for better
heat dissipation. Complex shapes and varying wall thicknesses can
also result in uneven heat distribution and differential thermal
distortion of the piston, so another objective is to simplify the
construction as much as possible including maximizing the symmetry
thereof about the central axis.
Also, another problem to consider is that the relatively rough
surface finish produced by the forging process can produce stress
risers, and this is especially critical in the high load areas of
the piston member such as in the thin wall sections and cavities.
Oftentimes these crack propagation areas are undetectable with
disastrous results.
Thus, what is needed is a high output engine piston assembly having
a piston member therefor which is capable of continuous and
efficient operation at combustion chamber pressures above about
13,790 kPa (2,000 psi), and preferably in the region of a bout
15,170 kPa (2,200 psi). Furthermore, the piston member should
preferably be forged from an alloy steel material having a
configuration substantially devoid of complex shapes to allow the
forging thereof. Moreover, the region of the upper portion of the
piston member and specifically the cooling recess region should
preferably have relatively thin, substantially constant wall
thicknesses for substantially even heat distribution and for
maximum cooling of the surfaces. Also, the surfaces of the cooling
recess should be machined surfaces of revolution for precise
dimension control between adjacent surfaces and especially between
the cooling channel and the ring grooves. The piston member should
preferably include symmetrical surfaces of revolution about the
central axis with the surfaces being free of imperfections that
could cause the propagation of cracks and so that differential
thermal distortion can be avoided.
The present invention is directed to overcoming one or more of the
problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the resent invention, a forged steel engine piston
member is provided that includes an upper main portion of generally
cylindrical shape and a relatively thin tubular wall depending from
the top surface thereof, and having a lower end surface, and an
inwardly facing wall surface extending upwardly from the end
surface. The upper portion also has an annular outwardly facing
wall surface spaced radially inwardly from the inwardly facing wall
surface and a transition portion connected thereto and to the
inwardly facing wall surface to collectively define an annular
cooling recess. The inwardly facing wall surface, the outwardly
facing wall surface and the downwardly facing transition portion
are all fully machined surfaces of revolution. The piston member
further has a lower portion including a pair of depending pin
bosses individually defining a bore and with the bores being
aligned.
In a further aspect of the invention, an engine piston assembly is
provided for an engine having a block, a cylinder liner received in
the block and defining a bore, and a cylinder head connected to the
block. The assembly includes a forged steel piston member having an
upper portion of a substantially cylindrical shape, a peripheral
top surface, and a relatively thin tubular wall depending from the
outer edge of the top surface and having lower end surface and a
inwardly facing wall surface extending upwardly from the end wall
surface. The upper main portion also has an annular outwardly
facing wall surface spaced radially inward from the inwardly facing
wall surface and a transition portion connected thereto and to the
inwardly facing wall surface to collectively define an annular
cooling recess. The inwardly facing wall surface, the outwardly
facing wall surface and the downwardly facing transition wall
surface are all fully machined surfaces of revolution. The piston
member further has a lower portion including a pair of depending
pin bosses individually defining a bore and with the bores being
aligned. A lower portion of the forged steel piston member includes
a pair of pin bosses blendingly associated with the recess and
individually having a bore therein. The piston assembly of the
present invention has a steel piston member with a non-complex
shape so that it can conveniently be forged and machined, is yet
has a cross sectional configuration that is capable of resisting
combustion chamber pressures in a range in excess of 13,790 kPa
(2,000 psi) and is lightweight.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic, fragmentary, transverse vertical
sectional view of an engine piston assembly constructed in
accordance with the present invention;
FIG. 2 is longitudinal vertical sectional view of a portion of the
piston assembly illustrated in FIG. 1 as taken along the line
II--II thereof;
FIG. 3 is an enlarged fragmentary portion of the top peripheral
region of the piston member shown in FIGS. 1 and 2 to better show
details of construction thereof;
FIG. 4 is a top view of the piston member shown in FIG. 2 as taken
along line IV--IV thereof;
FIG. 5 is a section view solely of the piston member shown in FIG.
2 as taken along line V--V thereof,
FIG. 6 is a top view solely of the piston skirt shown in FIG. 2 as
taken along line VI--VI thereof.
FIG. 7 is an enlarged fragmentary cross sectional view of the top
peripheral region of the piston member shown in FIGS. 1 and 2 which
shows the flow lines of a simple forged piston member with only a
portion of the cooling recess forged; and
FIG. 8 is an enlarged fragmentary cross sectional view of the top
peripheral region of the piston member shown in FIGS. 1 and 2 which
shows the flow lines of a forged piston member with a deeply forged
cooling recess.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIGS. 1 and 2, a diesel engine 10 of the
multi-cylinder type includes a bottom block 12, a top block or
spacer portion 14, and a cylinder head 16 rigidly secured together
in the usual way by a plurality of fasteners or bolts 18.
A midsupported cylinder liner 48 has a cylindrical upper portion 52
which is a stabilizingly supported by the top block 14 and defines
a piston bore 54 having a central axis 66. In this regard, cross
reference is made to U.S. Pat. No. 4,638,769 issued to B.
Ballheimer on Jan. 27, 1987 which further discusses the features
and advantages of the multipiece cylinder block with midsupported
liner discloses herein. The engine could however be of any
conventional design.
The diesel engine 10 further includes first and second cooling oil
direction nozzles 74 and 75 as is shown in the lower right portion
of FIG. 1. The first nozzle 74 is rigidly secured to the bottom
block 12 and is operationally associated with a conventional source
of pressurized oil, not shown, to supply a narrow jet of engine
lubricating oil substantially vertically in a preselected region of
an articulated piston assembly 76. The second nozzle 75 is also
secured to the bottom block, but is angularly inclined away from
the vertical to impinge a jet of cooling oil on another region of
the piston assembly 76.
The articulated piston assembly 76 of the diesel engine 10 includes
a forged upper steel piston member 78 and a lower forged aluminum
piston skirt 80 which are articulately mounted on a common steel
wrist pin or gudgeon pin 82 having a longitudinally oriented
central axis 84. A conventional connecting rod 90 having an upper
eye end 92 and a steel-backed bronze sleeve bearing 94 therein is
operationally connected to, and driven by the wrist pin 82.
As best shown in FIGS. 2 and 4, the steel piston member 78 has an
upper portion 96 of substantially cylindrical shape and a
preselected maximum diameter "D" as is illustrated. The upper
portion 96 has a fully machined peripheral top surface 98 that is
flat, or is located on a plane perpendicular to the central axis
66, and a recessed symmetrical crown surface 100 that in the
instant example is a fully machined surface of revolution about the
central axis 66. In general, the crown surface 100 has a centrally
located apex portion 102 elevationally disposed below the top
surface 98, a peripheral or outer axial surface 104 and an annular
trough 106 that smoothly blends with the apex 102 and the axial
surface 104.
As is shown best in FIG. 3, the piston member 78 further includes a
relatively thin tubular wall 108 that depends from the outer edge
of the top surface 98. The overall height identified by the letters
"LH" of the tubular wall 108 in this instant example was 31 mm. The
tubular wall defines in serially depending order fully around the
periphery thereof a first or top land 110, a top ring groove 112
having a keystone or wedge-like shape in cross section, a second or
upper intermediate land 114, an intermediate ring groove 116 of
rectangular cross section, a third or lower intermediate land 118,
a bottom ring groove 120 of rectangular cross section, and a forth
or bottom land 122 that is terminated by a lower radial fully
machined end wall surface 124. In the instant embodiment the
minimum elevational distance between the top surface 98 and the top
ring groove 112, indicated by the letters "TRH" was 5 mm. An
annular, generally axial, inwardly facing tapered wall surface 126
is also delineated by the wall 108 and extends upwardly from the
end wall surface 124.
The body portion 96 of the piston member 78 is additionally defined
by an annular radially outwardly facing wall surface 128 spaced
radially inward from the inwardly facing wall surface 126 and a
downwardly facing transition wall portion 130 that is blendingly
associated with the wall surfaces 126 and 128 to collectively
define an annular cooling recess 132 of a precisely defined
cross-sectional shape. It may be noted that the top of the cooling
recess 132 is in juxtaposed elevational relationship with the top
of the ring groove 112. It is also elevationally disposed directly
underneath the peripheral top surface 98 of the piston member 78
and within an elevational distance therefrom identified by the
letter E. In one embodiment the distance "E" was about 5.5 mm.
In actuality, the wall surface 128 of the instant example is
defined by an upper fully conical portion 134 having an inclination
angle "A" with respect to the central axis 66 of approximately
12.33 degrees as is shown in FIG. 3, and fully cylindrical portion
136 below it. On the other hand the wall surface 126 is fully
conical and has a inclination angle "B" of approximately 1.17
degrees. The inwardly facing wall surface 126, the outwardly facing
wall surface 128 and the downwardly facing transition wall portion
130 are all fully machined surfaces of revolution. It may be noted
that the radial thickness between the inwardly facing wall surface
126 and the innermost portion of the top groove 112 is slightly
larger than the radial thickness of the same wall surface and the
innermost portion of the seal ring groove 116. Hence, the latter
radial thickness is the most critical dimension, and in the instant
example the minimum acceptable value thereof was 1.74 mm.
Preferably, such value is 3 or 4 mm. The seal grooves 112, 116, and
120 are all fully machined surfaces of revolution so that the
critical cross-sections radially inwardly thereof are also
precisely controlled.
As an alternative, the annular cooling recess 132 could be of any
configuration to be forged such as the shallow recess shown in FIG.
7 or as an alternative the deep recess as shown in FIG. 8 As
further shown in FIGS. 7 and 8, the grain flows obtained by the
different depth recesses are shown by use of phantom lines. In the
alternative arrangement as shown in FIG. 8, it may be only
necessary that inwardly facing wall surface 126 be a machined
surface of revolution so that the critical cross section between
the surface and the seal ring groove 116 be precisely
controlled.
The piston assembly 76 also includes a top split compression ring
138 of a keystone shape which is received in the top ring groove
112, an intermediate split compression ring 140 of a stepped
rectangular cross section which is received in the intermediate
ring groove 116, and an oil ring assembly 42 which is received in
the bottom ring groove 120.
As shown in FIGS. 1 and 2, the steel piston member 78 also has a
lower portion 158 including a pair of depending pin bosses 160
blendingly associated with the outwardly facing wall surface 128 of
the cooling recess 132 and blendingly associated also with a
downwardly facing concave pocket 162 defined by the upper portion
and centered on the axis 66. The concave pocket is spaced
substantially uniformly away from the apex portion 102 of the crown
surface 100 so as to define a relatively thin crown 164 of
generally uniform thickness "C" as is shown in FIGS. 1 and 2. For
example, in the embodiment illustrated, the thickness "C" was
approximately 5 or 6 mm. A relatively thin and substantially
conically oriented web or wall 166 of a minimum thickness "W" is
defined between the trough 106 and juxtaposed annular cooling
recess 132. In the embodiment illustrated, the thickness "W" was
approximately 4 to 7 mm. Each of the pin bosses 160 has a bore 168
therethrough which are adapted to individually receive a
steel-backed bronze bearing sleeve 170 therein. These bearing
sleeves 170 are axially aligned to receive the wrist pin 82
pivotally therein.
Referring now to FIGS. 1, 2 and 6 the piston skirt 80 has a top
peripheral surface 172 in close non-contacting relationship with
the lower end wall surface 124 of upper piston member 78 with a
fully annular, upwardly facing coolant trough 174 defined therein.
It further has a slightly elliptical external surface 176
therearound which depends from the top surface 172. A pair of
aligned wrist pin receiving bores 178 are formed through the piston
skirt 80. The piston skirt 80 is thus articulately mounted on the
wrist pin 82 which is insertably positioned in both bores 178.
A pair of axially oriented bosses 184 are defined within the skirt
80 so that a corresponding pair of lubrication passages 186 can be
provided fully axially therethrough. The lubrication passages 186
provide for communication with the oil trough 174 and the cooling
recess 132. The lubrication passages 186 are positioned diagonally
opposite each other so that the skirt 80 can be mounted on the
wrist pin 82 in either of the two possible positions and so at
least one of them will be axially aligned with the first oil jet
nozzle 74. The skirt 80 is also provided with diagonally opposite,
semi-cylindrical recesses 188 which open downwardly at the bottom
of the skirt to provide clearance from the nozzles 74 and 76 when
the skirt is reciprocated to its lowest elevational position.
INDUSTRIAL APPLICABILITY
The unique forged steel piston member 78 in this application is
used with an articulate piston assembly 76. The articulated piston
assembly 76 is used in a high combustion chamber pressure engine 10
having a combustion chamber pressure of about 15,170 kPa (2200
psi). The piston member 78 allows the specific output to be
increased. As shown in FIG. 1, the articulated piston assembly 76
is used with an engine 10 having a mid-supported cylinder liner 48
and a two piece cylinder block 12,14 construction
In operation, during reciprocating movement of the piston assembly
76 the first nozzle 74 directs lubricating oil into the skirt
passage 186 aligned therewith. The oil jet continues upwardly
whereupon it makes contact with the inwardly facing wall surface
126, the outwardly facing wall surface 128 and the downwardly
facing wall portion 130 collectively defining the annual cooling
recess 132 of the upper portion 96 of the piston member 78. A
significant portion of the oil is caught by the skirt trough 174 as
the piston assembly is reciprocated where it is advantageously
splashed in a turbulent "cocktail shaker" action cooling the
peripheral surfaces 126, 128, and 130 of the cooling recess 132 and
thus the web 166 and the relatively thin tubular wall 108 defining
the ring grooves 112, 116, and 120. Simultaneously, the second
nozzle directs oil in a narrow column against the connecting rod 90
and against the concave pocket 162 or underside of the crown
164.
Referring to FIG. 3, it may be noted that the .[.op.]. .Iadd.top
.Iaddend.of the cooling recess 132 is in juxtaposed elevational
relationship with the top of the ring groove 112. It is also
elevationally disposed directly underneath the peripheral top
surface 98 of the piston member 78, and within an elevational
distance therefrom identified by the letter E. In one embodiment
the diameter D was 124 mm, and the distance E was about .[.5 to 5
mm.]. .Iadd.5.5 mm.Iaddend.. Thus, relatively thin, substantially
constant wall thicknesses are created for substantially even heat
distribution and for maximum cooling. The inner wall surface 126 is
a machined surface of revolution about the central axis 66 which
permits precise dimensional control and concentricity between the
bottom of the ring groove 112, 116, and 120 and the wall surface.
Dimensional control and concentricity between the bottoms of the
ring grooves and the surface 126 and especially the bottom of the
closest ring groove 116 to the surface 126 is extremely critical
because any deviation can materially weaken the tubular wall 78
resulting in cracking, uneven heat distribution and/or differential
thermal distortion. The inwardly facing wall surface 126, the
outwardly facing wall surface 128 the downwardly facing portion 130
defining the cooling recess 132 are all machined surfaces of
revolution about a central axis 66 eliminate any imperfections that
could cause the propagation of cracks and differential thermal
distortion. By machining the surfaces 126 and 128 and the
downwardly facing wall 130, wall thicknesses, concentricity and
surface finishes can all be precisely controlled. Alternatively,
with the arrangement shown in FIG. 8 with a deep forged recess 132,
it may only be necessary that the inwardly facing wall surface 126
be a machined surface of revolution for dimensional control and
concentricity with relation to the bottoms of the ring grooves 112,
116, and 120, and specifically the closest ring groove 116.
In addition to the dimensional constraints mentioned above, it is
to be appreciated that the articulated piston assembly 76 is
preferably manufactured in a particular way devoid of complex
shapes and by using certain materials. Specifically, the upper
steel piston member 78 is preferably forged from a chrome-moly
alloy steel material such as a basically 4140 modified steel
material. The lower aluminum piston skirt 80 is likewise preferably
forged an alloy aluminum material such as a basically SAE 321-T6
modified aluminum material.
The aforementioned alloy steel is particularly adaptable to Class
II forging procedures, and can provide an austenitic grain size 5
or finer which is highly desirable to resist the high compression
pressures above about 13,790 kPa (2,000 psi), and preferably above
about 15,170 kPa (2,200 psi). Etched cross sectional samples of the
forged steel piston member have indicated that the grain flow lines
therein are generally or broadly oriented in an inverted U-shaped
configuration that roughly approximates the shape of the piston
member portion shown in FIGS. 3, 6 and 7 and/or roughly aligns the
grain flow lines with the web 166 and the tubular wall 108, and
this contributes substantially to the cross sectional strength
thereof.
The aforementioned forged aluminum alloy has a high hardness,
excellent wear resistance, and a relatively low coefficient of
thermal expansion.
Other aspects, objects and advantages of this invention can be
obtained from a study of the drawings, the disclosure and the
appended claims.
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