Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This is a divisional application of &anadian Application Serial
No. 272,8~8, filed February 28, 1977.
This inven~ion relates to piston rings for internal combustion
engines, and more particularly to a compression ring for a reciprocating
piston internal combustion engine. The compression rings of a reciprocating
piston engine provide a sliding seal between the piston and cylinder wall
to prevent combustion gases fro~ leaking past the piston, i.e., gas blow-by.
More particularly, the present invention provides a compression ring which
has a circumferential relief of L-shaped cross section provided at its
upper-outer (dia~eter) portion to reduce *he bearing contact area of the
ring with the cylinder wall, and a corresponding circumferential relief
at its upp~r-inner (diameter) portion to help balance the ring against
twist and holp to properly seat it in its s~ating groove.
It is known to th~ prior art to provide co~npr~ssion rings whos~
outer face is beveled or chamfered to provide an upwardly and inwardly
inclined outer peripheral surface whereby the bearing contact area of the
ring with the cylinder wall within which it is disposed is reduced Such
reduction helps to diminish bearing friction of the ring against the
cylinder wall. It is further known to provide a bevel or chamfer on the
upper inside periph~ral surface of such rings. United States Patent 3,337,938
of H. ~. Prasse et ~1, assigned to the assignee of this application, shows
such an arrangement, in the context oE a torsion ring having a twisted
configuration as shown in Figure 9 of Prasse et al. The provision of sym-
metrical cut-outs to avoid uninten~ional torsion twisting of rings is shown
in United States Patent 2,~23,017.
One difficulty with sloping contact faces of the compression ring
is that wear of the bearing face reduces the effective back-pressure surface
against which combustion gas pressure may act during the compression and
power strokes to help balance the forces tending to thrust the ring against
the cylinder wall.
Attempts to reduce the bearing surface contact of the
~ :
765
ring against the cylind~ wall simply by reducing the axial width
of the ring and employing the full outer face ring surface in
bearing contact are handicapped because such structure eliminates
the back-pressure surface and because there is a limit to how
thin the ring can be made. That is, sound rincJ castings cannot
be reliably attained for rings of less than about .060 inch of
axial width.
Another difficulty of prior art rinys is that unintended
and disadvantageous torsional twisting of the xing is caused
by unbalanced ring cross section profiles, so that both the effect
of gas pressure acting on the ring and internal stresses set
up in the ring by the manufacturing process tend to twist the
ring out of a desired 1at seatin~ engagement with its associated
groove, resulting in poor se~ling and consequent c~as blow-by.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing and other
disadvantages by providing a piston ring having a circumferen-
tial~y extending recess formed in the upper-outer portion of the
ring to define a radial ledge which divides the outer axial
surface into a recessed outer face and an axial bearing surface.
The recessed outer face has an outside diameter which is less
than the outside diameter of the bearing sur~ace by an amount
which is at least equal to the radial wear depth of the bearing ~;
surface. The radial wear depth is that amount of reduction in
dimension (caused by we~r of the bearing surface) which will end
the useful operating life of the ring.
A circumferentially extending recess is also formed in the
upper-inner portion of tne ring. The respective dimensions and
configuration of the inner and outer recesses are selected to
balance the ring against torsional and gas pressure forces.
One result of the foregoing construction is that the area of
the bearing surface is considerably reduced ~hereby frictional
resistance to movement of the ring relative to the cy:linder wall
is grea~ly reduced. ~ur~her, the recessed outer face provides
a pressure surface on which combustion gases act to help reduce
diametral bearing pressure of the ring on the cylinder wall.
In addition, the inner peripheral recess is dimensioned relative
to the outer recess to balan_e the ring against torsion-inducing
internal stresses.
In one preferred embodiment, the inner peripheral recess is
similar or identical in configuration to the outer peripheral
recess so that an inner radial ledge divides the inner peripheral
surface into an offset inner surface whose inside diameter is
greater than the inside diameter of the ring, and an axial,
radially innermost surface, and the ring has an inverted T
cross section. The outer radial ledge (or its radially outer-
most portion if the ledge is sloped away from the horizontal) is
located between th~ upper and lower radial surface oE the riny
at a substantial axial distance down~ardly from the upper radial
surface, which distance is at least about 20~, preferably between
about 20 to 60%, of the axial width of the rin~. Accordingly,
the bearing surface comprises between about 80 to 40% of what
the total axial outer surface of the ring would be without the
outer recess. The recessed outer face thus stops short of the
lower radial surface. The ring is preferably made from a casting
or other base stock of uniform axial width so that both the upper
and lower radial surfaces are substantially flat and parallel
to each other.
In accordance with another- preferred embodiment of the
invention, any suitable hard, wear-resistant facing may be
applied to the bearing surface. The radially innermost extent
of the hard facing alloy defines the radial depth of penetration
of the alloy on the ring. Preferably, but not necessarily,
the hard facing alloy is deposited in a circumferential groove
formed for that purpose in the bearing surface. Preferably,
a ferro-molybdenum coating such as that of U.S. Patent 3,819,384
:;, ,` j~"5 , .
-3-
, j ~, .........
9~65
is used.
It is an object of the present invention to provide an improved
piston ring, more specifically to provide a split annular compression ring
of improved configuration exhibiting reduced frictional resistance to move-
ment against the cylinder wall, reduced blow-by of galses past the ring and
decreases in fuel consumption and hydrocarbons and carbon oxides exhaust
emissions.
It is another object of the present invention to provide a compres-
sion piston ring having formed at its upper-outer portion a recess of general-
ly L-shaped configuration to define a radial ledge, the radially outermost ~.
portion o which is positioned downwardly from the top radial suxface of the
ring a distance equal to between about 20 to 60% of the total axial width
o the ring, which ledge has n raclial dopth groater than the radial we~r depth
o the boaring surac0 of the ring, and to provide the ring with a recess in
its upper-inner portlon to minlmizo intorn~l torsional twi.~t stre~ses in the
ring.
It is yet another object of the invention to provide an improved
piston ring as hereinabove described which includes a hard facing coating on ;~
the axial bearing surface, preferably a ferro-molybdenum coating.
According ~o the present invention, then, there is provided an
annular piston ring or an internal co~nbustion engine having an upper radial
surface whlch defines the upper portion of the ring, a lower radial surface
which defines the lower portion o~ the ring and, extending between said upper ~ '!
and lower radial surfaces has, respectively, an outer axial surface which . :~:
defines the outer portion of the ring and an inner axial surface which defines ~ -
the inner portion of the ring, a ciTcumferentially extending recess formed in
the upper-outer portion of the ring to define an outer radial shoulder
having an outer radial ledge which divides the outer axial surface into a
recessed outer face and an axial bearing surface, the bearing surface having
a hard facing alloy thereon, the difference between the radius o the out-
side of the recessed outer face and the radius and said axial bearlng surface
being greater than the radial thickness o the hard acing alloy Oll the ring,
~ -4~
:
~797~iS
and a circumferentially extending inner peripheral relief formed in the
upper-inner portion of thc ring said relief having an inside diameter greater
than the inside diameter of the ring.
Other objects and advantages of the present invention as well as
the invention disclosed in Canadian Patent Application Serial No. 272,848
will be apparcnt from the following description o~ p:referred embodiments
thereof together with the accompanying drawings which form a part hereof
and wherein:
Figure 1 is a partial view in elevation of the top portion of a
piston for an internal combustion engine showing several piston rings
disposed in grooves in the piston head, including an embodiment of the
compression ring of the present invention in the topmost groove;
Pigure 2 is an enlarged section vlew taken alon~ lines II-II
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1~7~'765
of Fig. l;
Fig. 3 is a plan view of one embodiment of the ring of the
presen-t invention;
Fig. 4 is a view in elevation of the ring of Fig. 3;
Fig. 5A is a partial perspective view taken along arrow
A of section V-V of Fig. 3;
Fig. 5B is a view corresponding to that of Fig. SA but taken
along arrow B of Fig. 3;
Fig. 6A is a view corresponding to Fig. 5A showing another
embodiment of the invention;
Fig. 7 is a fragmentary cross sectional view of a piston
ring in accordance with one embodiment of the invention, receiv-
ed within its groove in a piston head disposed within the cylinder
of an internal combustion r~ciproca~incJ piston enc~in~;
E'ig. 8 is a view corresponding to Fig. 7 bu~ showing a t~st
piston ring not an embodiment of the invention;
Fig. 9 is a view corresponding to Fig. 8 but showing another
test piston ring not an embodiment of the invention;
Figs. 10 through 13 are graphs plotting minutes of engine
operation of, respectively, piston rings illustrated in Figs.
7, 8 and 9, against engine performance parameters, as follows: `
mani~old vacuum in inches of mercur~ (Fig. 10); fuel consumption
in pints per hours (Fig. 11); observed hydrocarbons in engine
exhaust in parts per million ~Fig. 12); and observed carbon
monoxide in volume percent (Fig. 13).
DETAILED DESCRIPTION OF THE DRAWINGS
Figs. 1 and 2 show a piston 10 of conventional type used in
reciprocating piston internal combustion engines. As such,
piston 10 is disposed within a cyiinder 12 which has a cylinder
wall 14. An annular space 16 is defined between cylinder wall
14 and the axial surface 11 of piston 10. As is conventional, a
top ring groove 18, a middle ring groove 20 and an oil xing
groove 22 are formed in piston 10. Top ring groove 18 receives
-5- ;~
( 1~7~76S
therein a split ~nnular compression or fire ring 24, middle
groove 20 receives therein an annular compression ring and oil
groove 22, which is usually wider -than the compressiorl grooves,
receives therein a conventional expander-loaded oil ring 28.
Referri~g to Figs. 3 and 4, compression ring 24 is shown
in its uncompressed state. As seen in Fig. 3, ring 24 is
approximately circular in configuration. ~owever, those skilled
in the art will recognize that conventional practice calls for
a split annular rinys to be made so that they are slightly out
of round in the uncompressed state, and in such a manner that
when the ring is compressed within its ring groove, the outer
diameter of the compressed ring adopts a more nearly circular
configuration.
~ shown in Fiy. 3, ring 2~ has an inside diamet~r indicated
by the dimension arrow ID, and an outside diameter indicated by
the dimension arrow OD. tThe dimension arrows ID, BOD and FOD
pass through the longitudinal axis L of ring 24 and may be
considered as applied to the ring in its compressed condition,
with gap 30 closed.) Dimension arrow FOD indicates the outside
diameter of the recessed outer face 40 (Figs. 4, 5A~. ~ecessed
ace 40 outside diameter FOD is seen to be less than ring 24
outside diameter OD by the distance 1, the radial depth o~ ledge
37 (Fig. 5A). Fig. 4 is drawn out of scale with its axial width
dimension exaggerated to more clearly show the structural features.
The axial width of ring 24 is indicated by the dimension arrow
W in Fig. 4.
Compression ring 24 is split and when the ring is uncom-
pressed the end faces formed by the split are spaced from each
other so that a gap 30 exists. A circumferentially extending
(outer) recess 32 is formed in the upper outer diameter of ring
24 as best seen in Fig. 4. A second circumferentially extending
tinner) recess 34 extends along the upper inside diameter of
ring 24. Ring 24 has a top radial surface 36 and a bottom radial
-6- - ,f
,~ .. ,:,.;
9765
surface 38, both of which are substantially planar, i.e., flat
without ~rooves or other recesses formed ther~in. Outer recess
32 is seen to be substantially L-shaped in cross section and
extends downwardly from upper radial surface 36 a dis~ance equal
to about 60% of the axial width W of ring 24.
Referring now to Fig. 5A and Fiy. 5B, circumferentially
extending outer recess 32 defines an outer radial ledge or
inwardly extending surface 37 which divides outer surface 33 into
a first outer axial bearing surface 42 and a second outer axial
recessed surface 40. Ledge 37 and bearing surface 42 define
an outer radial shoulder 39 projecting radially outwardly from
recessed outer face 40. It will be seen~ ther~fore, that the
first outer axial bearincJ surface 42 extends upwardly from the
low~r racli~l surEace 38 and terminates at the intermediate
inwardly extendiny surface 37. The intermediate surface 37
terminates at a second outer axial recessed surface 40 which in
turn terminates at the upper radial surface 36. The first outer
axial bearing surface 42 has a groove 46 formed therein. A hard
facing alloy 44 is deposited within groove 46.
Dimension arrow A in Fig. 5A indicates the extent to which
outer face ~0 extends downwardly ~rom upper radial surface 36
towards lower radial surface 38 along outer axial sur~ace 33 of
ring 24. Dimension arrow B indicates the corresponding extent
of bearing surface 42. Preferably, dimension A is 20 to 60
of dimension W, and dimension B accordingly is 80 to 40% of
dimension W, the sum of A and B being equal to W. Bearing surface
42 thus is reduced to approximately 40 to 80% of what it would be
- if there were no outer recess 32 and the full cylindrical outer
axial surface served at the beariny surface. It will be recog-
nized that in most cases the effective bearing surfaces are
reduced s'ightly by lapping of the edges of the bearing surface to
provide a desired "barrel" shape. This is shown i~ the rounded
edges 42A, 42B of Figs. SA, SB, and is typical also of prior art
i
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( 1~)79765
practice.
Reerring particularly to Fig. 5B, circumferential recess
34 is seen to have a flat, planar coniyuration which defines an
inner peripheral relief 47 having an inside diameter greater than
the inside diameter of the radially innermost surface 49 of ring
24.
Fig. 7 shows an enlarged schematic view in cross section
of ring 24 in place within its ring groove 18. Groove 18 has
a lower radial wall 18A, an upper radial wall 18C and an axial
bottom wall 18B. With ring 24 compressed within ring groove 18
so that gap 30 is closed, an outwardly actiny thrust represer.ted
by the arrow T urges ring 24 against cylinder wall }4 so that a
bearing, sliding contact is made between axial bear~ncJ surEace
~2 and wall 1~ as c~linder 10 reciprocates upwardly and downward-
ly ~as viewed in the drawing) within cylinder 12. The total
bearing area between ring 24 and wall 14 is seen to be but a
percentage (preferably 80 to 40%) of what it would be if the
entire outer axial surface 33, or almost the entire outer surface
33 were to be in bearing contact with wall 14 as is the case, for
example, with the test ring (not an invention embodiment) of
Fig. 8. The wall thickness of the ring 2~ is indicated by the
dimension arrow t, and the width by dimension arrow W. S is
the radial thickness of upper radial surface 36, 1 is the radia}
depth of radial ledge 37 and a is the angle included between the
surface of inner peripheral relief 47 and the plane of upper
radial surface 36. The angle a may be referred to as the inner
relief angle. The axial width of radially innermost surface 48
is shown by the dimension x. As shown in Fig. 7, the inner axial
surface of the ring 24 includes a first inner axial surface
portion 49 (Fig. 5A) or 71 (Fig. 6A) which extends upwardly a
distance y from the lower radial surface 38 to an intermediate
circumferential line 51 (Fig. 5B) or 73 ~Fig. 6A) and is in
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9765
confronting relation ~ith the bottom 18B of the groove 18 in the
piston 10. A second inner peripheral relief surface portion 47
extends between the termination of the flrst inner axial surface
portion 49 and the upper radial surEace 36. The diameter of the
inner peripheral relief surface 47 at its termination at the upper
radial surface 36 is greater than the inside diameter of the ring
at the circumferential line 51.
Fig. 8 shows a test ring (not an invention embodiment) in
which a compression ring 50 has substantially the entire outer
1~ axial surface thereof (less beveled edges) in bearing contact
with cylinder wall 14. The wall thickness of ring 50 is shown
by dimension arrow t, and the width by dimension arrow W. The
total thrust of ring 50 bearing outwardly agains-t cylinder wall
1~ is indicated by the arrow 'r. The laryer b~aring surEace
53 of ring 50 in contact with wall 1~ provides a cJreatex fric-
tional resistance to movement of ring 50 and its associated piston
10 relative to cylinder 12.
Referring again to Fig. 7, the short unnumbered arrows shown
directed against the various upper surfaces of ring 24 repres,ent
the force vectors of compressed combustion gases entering annular
space 16 and acting on ring 24. Such forces are exerted during
the compression and power strokes of the piston. ~s shown in
Fig. 7, the net effect of gas pressure acting against surfaces
37, 36, 47 and 48 is to augment the outwardly acting thrust
represented by the arrow T. This net outwardly acting thrust is
at least partically offset by the force of the gas acting agains-t
recessed outer face 40 as indicated by the arrow impinging thereon.
Thus, the face 40 causes the tendency of the exploding combus-
tion gases to provide an outwardly acting thrust on ring 24 to
be considerably reduced. This substantially reduces the diametral
pressure of the ring against the cylinder wall. It will be notedthat with the full bearing face contact of test ring 50 of
Fig. 8, no equivalent to recessed outer face 40 is provided, so
that the entire effect of the combustion gas pressure is to
_g_ ;,.,".. .
( ~79765
augment the outward thrust r~ of ring 50 a~ains-t surface 14.
Consequently, with other thinys equal, T of ring 24 is less than
T' of ring 50 so that bearing pressure and frictional resistance
is lessened.
Referring again to Fig. 7, as axial bearing surface 42
wears do~7n in use, the compression tension of ring 2~ will cause
the ring to correspondingly expand outwardly to maintain bearing
surface 42 in bearing sliding contact with cylinder wall surface
14. The section line P-P shows, in exaggerated fashion for
clarity of illustration, the relative position of cylinder
wall 14 to ring 24 after a considerable amount of wear has been
sustained by axial bearing surface 42. Because of the L shaped
configuration o~ the outer circumferential recess 32, the effec-
tive ~as pressuxe surface provided b~ rec~ssed o-lter face ~0 is
una~fected recJardless o~ th~ extent of wear ~f bearincJ surface
42. In this manner, the beneficial gas pressure balancing effect
provided by recessed outer face 40 is not adversely affected
by wear sustained by bearing surface 42. For this reason, it
is an important feature of the invention that the outer diameter
~FOD in Fig. 3) of the recessed face 40 is less than the outside
diameter (OD in Fig. 3) of the ring by an amount which is at
least as great a~ the radial wear depth of the ring bearing sur-
face. In this manner, as the bearing surface ~42 in Fig. 5A
and which, in all cases, defines the outside diameter of the ring)
wears down in use, no part of the effective gas surface provided
by the recessed outer face (40 in Fig. 5A) is brought into contact
with cylinder wall 14. Usually, the radial wear depth is less
than the radial depth of the hard facing coating (~4 in Fig. 5A)
applied to the bearing surface of the ring. Preferably, the ra- -
dial depth l of the ledge (37 in Fig. 5A) is much greater than
the radial wear depth of the bearing surface, so the recessed
face (40 in Fig. 5A) is unaffected by bearing surface wear.
Otherwise stated, preferably the outside diameter of the outer
.,~ . .,.~. , ::
- 1 0- , , , , ~ ;,;
..
. .. . .. . , ...... .. ~
1'7~765
~, .
recessed face terminates short of the depth of radial penetration
of the hard facing alloy on the ring bearing surface. The bear-
ing surface is usually circumferentially grooved to receive the
alloy, although obviously it need not be ancl the hard facing
alloy can be deposited on an ungrooved bearing surface.
While in the preferred embodiment illustrated, ledge 37 is
shown approximately parallel to the radial surfaces 36, 38 and
approximately perpendicular to recessed surface 40, such arrange-
ment is not necessary in accordance with the invention. The
radial ledge and recessed outer face may, of course, intersect
each other at an angle other than 90. In general, the outer
recess ~32 in Fig. 5A) may have in accordance with the invention,
a cro~s section proile formed o two or more intersecting line
~egments. The line segments may be straicJht or even curved,
or some straight and some curved. For example, the profile of
recess 32 in the Fig. 5A embodiment may be modified by a curved
fillet formed at the intersection of ledge 37 and face 40; ledge
37 may be sloped upwardly or downwardly towards face 40; face 40
may be sloped inwardly or outwardly; face 40 andJor ledge 37
may be formed with other than the straiyht-line profile illustrat~
ed. All such modifications are within the scope of the invention
provided that the recessed outer face is recessed sufficiently
with respect to the bearing surface that the ~7ear o~ the bearing
surface to the radial wear depth does not affect any significant
reduction of the effective gas surface provided by the recessed
outer face. It will be appreciated that if the design of the
ring is such that ledge 37 slopes upwardly towards the recessed
face (4). The effective gas area provided by the recessed face
is slightly reduced; if it slopes downwardly the effective gas
area of the recessed face is slightly enhanced.
This is to be compared with the test ring of Fig. 9, wherein
a ring 52 having a bearing face conforming to the priox art has
sloped outer face 54 which provides a bearing surface ~6 of
, .
,. , ~ .,, '.' ~ "!j
7976S
reduced area. The wall thickness of ring 52 is shown by the
dimension arrow t, and the width by dimension arrow W. The net
outwardly acting thrust of riny 52 aginst cylinder wall 14 is
indicated by the arrow T". Combustion gas pressure foces ac~ing
on ring 52 are indicated by the shor-t unnumbered arrows shown
in Fig. 9. Assuming that axial bearing surface 56 of Fig. 5A is
identical to axial bearing surface 42 of ring 24 in Fig. 7, it
will be appreciated that frictional resistance of ring 52 is
reduced and that sloped outer face 54 provides an effect:ive gas
surface tending to balance a por-tion (but a lesser portion than
that provided by ring 24) of the gas forces acting outwardly on
the ring. However, as face S6 sustains wear, the relative posi-
tion o~ cylinder wall 1~ chanc~es as indicated by line P'-P' r in
exa~gerated ashion for clariky o~ illustration. It will be
observed that with lncreasin~ wear o~ beariny sur~ace 56 t~e area
o sloped outer face 54 available to act as an effective gas
pressure surface to balance the outwardly acting gas pressure
forces is considerably reduced and in an extreme case would tend
towards being entirely eliminated as the entire outer axial sur-
face of ring 52 comes into bearing contact with cylinder wall 14.
It should be noted that conventional prior art practice is to pro-
vide only a very sliyht slope, usually one to three degrees,
to sloped face 54.
As is known in the art, it is sometimes desired to provide
a slight torsional twist to a piston ring rather than to strive
for a flat configuration. Provision of the circumferentially
extending outer recess 32 would normally cause the piston ring
such as ring 24 to "dish" in a reversed torsion manner, that is,
the inner periphery of the ring would tend to be twisted upwardly
and the outer periphery would tend to be twisted downwardly.
Such twisting is of course relatively slight yet nonetheless it
is importatn in changing the angle oE contact of the ri.ng with
the cylinder wall and in raising the ring from flat seating contact
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'79765
within its yroove. In accordance with the present inve~-tion, it
is desired to reduce or substantially eliminate such torsion
twisting of the ring to enhance flat sealing contact of lower
radial surface 38 against the bottom radial wall 18A of groove 18.
Calculations of the diametral force against the wall of the -~
cylinder of a number of differently confiyured rings were made
and are summarized in the following Table. The diametral force
is the force with which the ring bears against the cylinder wall
at peak combustion pressure.
io TEST RESULTS
Dimensions Common To All Rings
Bore Diameter = 4.000 inches
Wall thickness ~t in Figs. 7, 8 ~ 9) = 0.182 inch ~.177 .187 inch,
~S~E int. wall)
Wid~h (W in Fig~. 7, 8 ~ 9 ~ 0.078 inch
Peak Combu~tion = 800 psi
Ring Diametral Tension - 0 ~dead ring)
Diametral Force Calculated for Different Rings
Bearing surface (42 Fig. 7 Type Fig. 7 Fig. 8 Fig. 9
20 in Fig. 7, 53 in RinG but with- Type 'l'ype Type
Fig. 8, 56 in Fig.out an inner Ring Ring Ring
9) as percent ofcircumferentially
total cylindricalextending recess
outer axial surface
of ring
CalculateA Diametral Force - LBS. I
10% ~ 2~-~ ;
40~ 2~7 264
50% - - - 33~- j
60% 402,407* - - - j
80% 558 575
100% - - 718-730**
* For 2 rings having different depth of radial ledge (1 in ~ig. 7)
but otherwise identical.
** For 4 rings having differently sized inner circumferentially
extending recesses, but otherwise identical.
The reduction in diametral force when the bearing surface
is reduced to 10% of the theoretical cylindrical outer axial
surface is so great that effective sealing against gas blow-by
is not attained. On the other hand, when the bearing surface
'I , .
-13- ~ J
7~3'765
is more than 90% oE theore-tical, siynificant reduction in the
diametral pressure and frictional resistance is not attained.
It has been found that optimum results of a substantial
reduction in frictional resistance and yood sealing ayainst gas
blow-by are obtained when the bearin~ surface comprises more than
10% and less than 90%, preferably, 40 to 80%, of the theoretical
cylindrical outer axial surface of the rincJ, i.e., preferably
40 to 80% of what the bearing surface would be if there were no
recessed outer face formed therein. (The preferred range cor-
responds to the outer radial ledge beiny positioned 60% to 20downwardly from the top radial surface.)
In a preferred construction, the axial width W is about
.078 inch, and the outer radial ledye is positioned about .038
inch downwardly from the top radial surEace, or ~bou~ ~9~ of the
axial wi~th.
It has further been found that, surprisingly, good sealing
against gas blow-by and emissions reduction is enhanced with the
ring of the invention despite the reduced diametral ~orce of the
ring. ~The reduced bearing surface of course provides an
increased diametral pressure for a given diametral force, which
helps to offset the reduced force.) This surprising result may
also be aided by making the lower radial surface of ~lat, undished
configuration and maintaining it in good sealincJ contact with the
bottom of the ring groove in which the ring is seated by elimina-
ting torsional thrust in the ring.
Referring to Fig. 7, in order to balance the torsion twistin~
effect of circumferential recess 32, an inner circumferential
recess 34 is provided. Recess 34 is dimensioned as desired either
substantially to eliminate or reduce to a desired level the
reverse torsional twist tendency imparted to riny 24 by outside
circumferential recess 32. Inside circumferential recess 34 may
be dimensioned not only to overcome the reverse torsional twist
tendency but to avoid yiviny to the riny a net normal torsion
--1 ~-- . .; .. " ~
-- (
~97~5
twist tendency. Th~t is, to cause the ring 24 to be dished in
suc~ a manner that the outer periphery portion thereoE is twisted
upwardly thereof and the inner periphery portion -thereof is
twisted downwardly. (Illustra-tions of reverse torsional twist
and normal torsional twist are given respectively, in Figs. 6 and
9 of the aforementioned U.S. Patent 3,337,938.)
Generally, a preferred embodiment of the invention has the
effective inner and outer circumferential extendiny recesses
32 and 34 so dimensioned that the torsional twist tendency of the
ring is substantially balancedout and a flat, non-dished ring
is produced with a lower radial surface 38 which seats in flat,
planar contact with bottom wall 18~ of its associated groove 18.
In a pxeferred embodiment as illustrated in Fig. 7, inner xelie
angle a is 25, the radial thickness s of upper r~dial surface 36
is one-third of t, the wall thickness, and the radial d~pth 1
of radial ledge 37 is equal to x, the axial width of xadially
innermost surface 48. The sum of A plus B (the axial widths,
respectively, of outer face 40 and bearing surface 44) are equal
to W, the total axial width of ring 24. A is e~ual to between ~:
about 20% to 60~ of W. In a preferred specific embodiment, W
equals .078 inch, t equals .182 inch and x and 1 each e~ual .02 ;.
inch, with a eclual to 25, and A e~ual to 60~ of W. Obviously,
any dimensions may be employed as required so long as the precepts
of a reduced bearing surface, recessed outer face, and balancing J,
inner recess or relief are followed.
Referring now to Fig. 6A, there is shown another embodiment e
of the invention comprising a piston ring 58 having an outer
circumferentially extending recess 60 and an inner circumferential-
ly extending recess 62, recesses 60 and 62 both being of sub-
stantially L-shaped cross section. Accordingly, ring 58, has an
outer radial shoulder 64 and an inner radial shoulder 66, and
a recessed outer face 68 and a recessed or offset inner :Eace 70.
Shoulder 64 provides an outer radial edge 67 and shoulclex 66 pro-
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3'76$
vides an inner radial edge 77. Top radial surface 72 extends
between faces 68 and 70 and bottom radial surface 74 ex-tends
between the radially innermost and radially outermost portions
of ring 58. A groove 76 is formed within axial bearing surface
78 provided by the radially outermost portion of outer radial
shoulder 64. Groove 76 is filled with a hard facing material 18.
Ring 58 is seen to have an inverted-T cross section. The radial
depth of outer ledge 67 is shown as 1, that of inner ledge 77 as
1'. The axial width of ring 58 is shown as W, that of recessed
outer face 68 is shown as ~, that of axial bearing surface 78
is shown as B. The axial width of recessed inner face 70 is shown
as A', and that of innermost axial surface 71 is shown as B~.
may or may no~ be equal to ~', although i~ is in a preferred
embodiment. Similarly, 1 m~y or may not be equal to 1', althouyh
it iS in a preferred embodiment. A plus B e~uals W, and Al
plus Bl equals W. It will be appreciated that ring 58 of Fig.
6A provides the same advantages of the invention as does ring
24 in providing a reduced bearing surface 78 and an effective t
surface 60 against which combustion gas pressure may act to off
20 set at least partially the outwardly acting thrust effects of
combustion ~as pressures. Ring 58 also provides the torsion
tWiSt balancing features. It will be appreciated that the respec- ~
tive circumferentially extending recesses 60, 62 of ring 58 may
be either identical in dimensions or slightly different in
dimension.
In operation, compression piston rings in accordance with P
the invention have shown distinct advantages over prior art com-
pression rings. For example, piston rings of the embodiment of
the invention illustrated in Fig. 7 were tested ayainst prior
art rinys of the embodiment illustrated in Figs. 9 and 10. The
Fig. 7 type rings were dimensioned such that radial shoulder 37
was located at a point 60~ of the to-tal axial width below the
upper radial surface.
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Comparison tests were carried out by utilizing rings of 'the
above described configuration in a Buick 455 cubic inch displace-
ment engine which was run at given speed and horsepower output
in a series of rungs utilizing, respectively, rings according
to Figs~ 7, 8 and 9. Manifold vacuum pressure, fuel consumption,
and the hydrocarbons and carbon monoxide content of the engine
exhaust were continually monitored during engine operation. The
result of the test are shown in the graphs of the Figs. 10, 11,
12 and 13.
Referring to Fig. 10, manifold vacuum in inches of mercury
is plotted against minutes of operation. The graph shows manifold
vacuum measured over 3 hours of engine operation under identical
operating conditions in the same engine save for the employment of,
respectively, the Figs. 7, 8 and 9 rings as the top compression
rings o~ the engine. It will be noted that a consistently higher
manifold vacuum is attained when emplo~ing the piston rings of
the invention, i.e., the Fig. 7 embodiment thereof indicated by
the line A. Lines B and C show, respectively, the manifold
vacuum in inches of mercury measured when employing the test
piston rings of Figs. 8 and 9.
Fig. 11 shows the rate of ~uel consumption measured at 15
minute intervals during engine operation. Generally, in operation
as indicated by line A with the Fig. 7 embodiment of the invention,
a generally lower rate of fuel consumption was re~uired by the
engine. This is attributed to the reduced frictional resistance
between the ring and the cylinder wall an a more effective seal- I
ing by the balanced, flat seating ring of Fig. 7.
Fig. 12 shows the observed hydrocarbons in the engine ex-
huast in parts per million. Significantly cleaner exhaust in
terms of hydrocarbons content when employing the piston ring in
accordance with the invention is indicated by line A. Lines B
and C both show substantially higher hydrocarbon content for the
Fig. 8 and 9 test rings.
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'`' ' ` 107~76S
Fig. 13 shows the observed carbon monoxide present in the
enyine exhaust as percent of the total engine exhaust. The
favorable results provided when employing the piston ring of the
invention is indicated by the line ~. Lines B and C both show
noticably hiyher carbon mono~ide contents when using the rings of
Figs. 8 and 9.
As indicatecl by visual examination of all the tested rinys
after the engine operation, it appears that the reasons for the
superior showing of the riny of Fig. 7 as compared to the other
two rings tested was its better facility for pressure balancing
despite its lower diametral force, as compared to the rings of
Figs. 8 and 9. The low inherent twist of the balanced inside and
outside diameter recesses enables the ring of the Fig. 7 embodiment
to rest flat on the bottom wall of the groove,, and this appears
to be responsibl~ for recluc.~ng the amount oE combustion gas which
b~-passes the rings. 'rhe rin~s oE Figs. 8 and 9 exhibited s.iyns
of a torsional twist which, while possibly desirable in-some appli-
cations, does not appear to provide good sealing as combustion
yases drive the ring dowr~wardly and rearwardly in the groove.
Piston rings in accordance with the invention can be made r
as follows. For rinys to be grooved to receive a hard faciny
alloy, circumferential grooves are cut in the bearing surface of ',
the ring. This may be accomplished in the known manner by en-
gaging cuttincJ tools with a plurality of rings which are clamped
on an arbor to from a stacked cylinder of rings. After the bear- '
ing surface grooves are cut, the surface of the stacked rings is
sprayed with a hard facing alloy. The hardened alloy s then
ground down to expose the ring metal on either side of the
grooves, leaving the grooves filled with the hard facing alloy.
The outer circumferential recesses may then be cut in the rings
in a manner similar to that in which the grooves were cut. The
inner circumferential recesses may similarly be cut by a plura-
lity of cutting tools inserted through a hollow shaft on the
mounting arbor i! Alternatively, to cut -the inner and outer re-
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~.~'7~7~5 ~.
cesses, individual rings may be held in a clamping device and the
inner and outer circumferential recesses cut simultaneously by a
pair of oppositely facing cutting tools.
While specific embodiments of the invention have been des-
cribed in detail, it will be appre~iated that numerous modifica-
tions thereto can be made by those skilled i:n the art after
reading and understanding of the foregoing s]pecification. It is
intended to include all such modifications and alterations within
the scope of the appended claims.
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