Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
PISTON RING
BACRGROUND OF THE INVENTION
The present invention relates to piston rings, and
more particularly to a parted annular piston ring
structure having a wear-resistant facing or coating on the
ring bearing surface and an overlap-type sealing joint at
the ring gap.
It has heretofore been recognized that parted annular
rings having a wear coating on the outer radial surface
may be advantageously employed as top or compression
piston rings in a reciprocating piston internal combustion
engine. Examples of such rings are disclosed in U.S. Pat.
No. 3,133,739 to Marien and U.S. Pat~ No. 2,266t692 to
Olson. It has also been found desirable to provide
overlapping joint designs at the ring gap in piston
compression rings to obtain improved sealing at the ring
gap with resultant reduction in so-called blow-by of
combustion gases. Example~ of such seal joint designs are
shown in the U.S. patent to Raworth, No. 615,902.
However, it has been found that the overlap-type gap
joints previously proposed to provide effective sealing
cannot be utili~ed with wear-coated rings of conventional
design without potential chipping and damage to the wear
coating in the joint area during ring manufacture. It has
been proposed to leave the joint area uncoated, but this
can result in ineffective sealing and damage to the
engine.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention
to provide an improved parted annular piston ring which
combines the advantageous characteristics of wear-coated
piston rings with the improved blow-by sealing
characteristics of overlapping-type joint desi~ns; and
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wherein the wear-coating extends completely
circumferentially around the bearing surface of the ring.
Other objects, features and advantages of the
invention will becom~ apparent from the following
description, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a piston ring
constructed in accordance with the principles of the
present invention;
FIG. 2 is a fragmentary vertical sectional view taken
on the line 2-2 of FIG. 1;
i FIG. 3 is a fragmentary view of a portion of the ring
illus rated in FIG. 2 but enlarged thereover;
FIG. 4 is a fragmentary vertical elevational view
looking in a direction of the arrow A of FIG. l;
FIG. 5 is a fragmentary vertical sectional view taken
on line 5-5 of FIG. l;
FIG. 6 is a fragmentary top plan view illustrating
the parted ends of the ring in an exaggerated free state
condition;
FIG~ 7 is a bottom plan view similar to FIG. 6;
FIG. 8 is a fragmentary perspective view of the
parted ends of the top surface of the ring,
FIG. 9 is a fragmentary perspective view illustrating
the parted ends of the bottom surface of the ring; and
FIG. 10 is a fra~mentary view~ similar to FIG. 3, of
a portion of another piston ring constructed in accordance
with the principles of the present invention.
ETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring in more detail to the drawinys, FIG. 1
illustrates a piston ring 20 which embodies the principles
of the invention in one exemplary presently preferred form
for use as a top compression ring in a diesel engine. As
best seen by comparing FIGS. 1-4, ring 20 is of the type
having a barrel face outer periphery 22, i.e., the outer
peripheral face 22 of the ring has a uniform curvature
about a ra~ius R (FIG. 2). The cross sectional
configuration of ring 20 is of the keystone type, i.e.,
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the top and bottom sides 24 and 26, respectively, of the
ring 20 are tapered so as to converge toward one another
inwardly of the ring. The inner periphery 31 of ring 20
extends parallel to the axis thereof.
~ s best seen in FIGS. 3 and 4, the outer face 22 of
the ring has a circumferentially extending groove defined
by a root face 32 and upper and lower edge surfaces 34 and
36, respectively. This groove is filled in accordance
with known techniques, e.g. plasma spraying with a hard
wear-resistant material, such as chromium, to provide a
band 38 extending circumferentially around the outer face
of the ring 20. The body of the ring 20 is made by
conventional methods such as centrifugal casting, and--
comprises a ferrous metal such as ductile iron or steel.
! In accordance with one embodiment of the present
invention, the wear band 38 is offset axially of the ring
20 such that its center is disposed slightly below a
central plane P of the ring (FIGS. 2 and 3) so as to form
upper and lower iron lands 40 and 42, respectively, (FIGS.
3 and 4), which are une~ual in width lmeasured axially of
the ring 20)~ The radius R is centered uporl the plane P.
It has been found that both upper land 40 and lower land
42 are narrow enough in such embodiment to minimize any
scuffing tendency between the lands and the cylinder bore
of an associated engine (not shown). The aforementioned
barrel face 22 further reduces any scuffing by positioning
the lands 40 and 42 away from the opposing cylinder wall
(not shown~.
In accordance with another feature of the present
invention, ring 20 is provided with an angle-type over-lap
joint at the ring gap to reduce blow-by leakage in the
engine. The joint design is a modified form of the type
generally shown in FIGS. 6 ~nd 7 of the aforementioned
Raworth U.S. Pat. No. 615,902. ~hus, as best seen in
FIGS. 6 9, one of the parted ends of ring 20 is provided
with a tongue 50 which protrudes circumferentially from a
radially and axially extending end face 51 toward the
other end of the ring. The other parted end of the ring
20 is provided with a tongue-receiving, complementarily
.
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angled recess 54 (FIG. 8). When ring 20 is compressed to
operating diameter, as when the same is disposed in
operative position in its corresponding top compression
ring groove of a piston and the piston is assembled into
the associated cytinaer bore of an engine, tongue 50
underlies and slidably overlaps the opposite parted
5 recessed end 54 of ~he ring 20. This normally overlapped,
operative condition is illustrated in FIGS. 1, 4 and 5.
Referring now to FIG. 10, a further preferred
embodiment of a piston ring embodying the principles of
the present invention is illustrated at 90. The ring 90
is of the type having a barrel face outer periphery 91;
the outer peripheral face 91 has a uniform curvature ~bout
a radius Rl (FIG~ 10), whichl unlike the face 22 of the
ring 23 shown in FIG~ 3 whsse radius of curvature R is
centered on plane P, is not centered on a central plane P'
of the ring 90. In the ring 90, a wearband 92 of
wear-resistant material is offset axially of the central
plane P'; its centerline lying in a plane C is disposed
slightl~ therebelow so that the radius of curvature R' is
centered upon plane C. The maximum outside diameter of
the ring 90 therefore falls upon the center, taken axially
of the ring 90, of the wearband 92. Iron lands 93 and 94,
which form the upper and lower boundaries, respectively,
of the band 91 are made unequal in width (measured axially
of the ring 90) and, for example, have dimensions
substantially equal to those previously described for the
ring 20 shown in FIG. 3. Likewise, top and bottom sides
95 and 96, respectively, and all other features of the
ring 90 are substantially identical to those of the ring
20, as described above and in the discussion which
follows. It has been found that a preferred piston ring
of the present invention having an offset barrel face,
such as the ring 90, is especially advantageous for
reducing the so~called blow-by of combustion gases, in
service, and can also provide unexpectedly good
wear-resistance since this feature helps to assure that
the band of wear-resistant material will be in contact
with the cylinder wall of the engine at all times.
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Referring again to FIG. 9, the angle seal joint of
the ring 20 can be made by a conventional milling
operation which cuts away the material from the end of the
ring to form tongue 50, the milling cut simultaneously
producing the angled top surface 52 of tongue 50 as well
as the radially and axially extending end surface 51. The
upper end of surface 52 terminates at the
circumferentially extending edge 56 which is located
approximately in the middle of upper land 40 of the
tongue end of the ring. The lower, inward end of angled
; surface 52 terminates at an edge 58 extending
circumferentially of the ring close to but radially
outwardly of the inner edge 60 of the inner periphery 31
of the ring~ The wear-resistant band 38 extends all the
way to the axia7ly extending outer edge 62 of tongue 50,
and the end face 64 of tongue 50 is disposed on a raaial
plane parallel to the axis of ring 20.
The recess 54 in the other parted end of ring 20 can
likewise be formed by a milling operation to produce an
angled surface 70 and associated side face 72 of the
; recess 54 ~FIG. 8). The outer upper edge 74 of surface
70, like edge 56, extends circumferentially into the
middle of upper land 40 (FIG. 8). The lower, radially
~' inward edge 76 of surface 70 also extends
circumferentiall~ of the ring 20 and is located
substantially coextensively with edge 58 in the overlapped
condition of the ring (FIG. 5). The end face 78 (FIGS.
6-8) of the recessed end of the ring extends essentially
parallel to face 51 to which it is juxtaposed in the
overlapped, operative condition of ring 20.
The provision of the larger width upper land 40 of
ring 20 through which the angle seal joint breaks out at
the outer periphery of the ring 20 at edges 56 and 74
~FIG. 8) leaves an upper land extension 40a extending
along tongue 50 from the outex edge of face 51 to end face
64 (FIG. 7) and an upper land extension 4Gb extending
along the outer periphery of the recessed end of the ring
between faces 72 and 78. Preferably, land extension 40a
has an axial dimension ranging from substantially one to
.
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two times the axial dimension of land extension 4~b. It
is a]so preferred that land extension 40b (FIG. 8) ~e at
least equal to or slightly greater in axial dimension than
lowPr land 42 of ring 20. Surfaces 52 and 70 (FIGS. 5, 8
and 9) lie in planPs at an acute angle with respect to
plane P and extending essentially diagonally of the ring
body cross section.
In fabrication of the ring 20, after the angle seal
joint is milled in the parte~ ends thereof, a plurality of
such rings are fixtured on an arbor and plasma-spray
coated with the hard, wear-resistant material. The
spray coated surfaces are then ground to expose lands 40
and 42 separated by the band 38. Edges 74 and ~6 of
extensions 40a and 40b are then located outside Gf the
xing surface portion filled by the sprayed metal. Thus,
when expanding force is applied to the sprayed rings to
part the ends, the only area where chippa~e of
wear-resistant band 38 is apt to occur is at the edges 62
and 80. The effect of such chippage along the axial edges
62 and 80 is minimized or eliminated by a subsequent gap
grinding operation. This is feasible because of the
relatively large dimensional tolerances permissible in the
free gap dimensions, which in turn allows metal removal
from surfaces 64 and 72 ~and coating edges 62 and 80)
without exceeding gap tolerances~ Xn prior attempts to
utilize an angle-seal overlap joint in wear-coated rings
~5 where the edges 56 and 74 were disposed within the hard
coating metal, the angle surfaces 70 and 52 could not be
machined to remove chippage while main~aining minimum
clearance conditions between surfaces 52 and 70 to control
gas leakage through *he overlapped gap. Typically, in the
exemplary rings heretofore-mentionedr the clearance
between these overlapping surfaces is maintained between
the limits of 0.03 to 0.13 mmO
It will be understood that the angle-type joint
design per se is operative to seal in the direction from
the top side of the ring to the bottom side, the top side
normally being marked ~UP" and with a ~machine dash" 84
(FIGo 6) so as to be oriented in assembly in the direction
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of the cylinder combustion area. Thus, with the top side
of ring 20 installed facing upwardly toward the top of the
piston, sealing by the ring joint is in the upward-to-
downward direction. It is also to be understood that
upper land 40 is preferably made wider than the lower land
42 to allow the angle seal joint to break out in the land
S 40 while still leaving land extensions 40a and 40b of
sufficient width ~o insure edge strength~ Nevertheless,
and although not presently preferred, the lower land 42
could be made equal in width to upper land 40 in
appropriate circumstances. Although the invention has
been described in conjunction with chromium-filled rings,
the principles of the invention are equally applicable to
rings having other wear-resis~ant materials filling the
groove, such as molybdenum, ceramics, aluminum oxide,
oxides of chromium, chromium carbide or titanium ~arbide.
In the foregoing description and the appended claims,
directional terminology such as "top", "bottom"~ "upper~
and ilower" is used by way of description and not by way
of limitation with reference to the preferred and
hereinabove described orientation of the ring relative to
the associated piston in an application where the piston
reciprocates vertically and the ring is used as an upper
or compression seal.
