CA1079765A - Low friction balanced piston ring - Google Patents

Abstract

ABSTRACT

A low friction piston ring of split annular construction has a circumferentially extending recess formed at its upper outer portion to define an outer radial ledge which divides the outer axial surface of the ring into a recessed outer face and a reduced (as compared to the total outer axial surface) bearing surface. The bearing surface preferably has a wear resistant coating thereon. The outside diameter of the recessed outer face is less than the outside diameter of the bearing surface by an amount at least equal to the radial wear depth of the bearing surface. A peripheral recess is also formed at the upper-inner portion of the ring to reduce or eliminate torsional twisting of the ring. The ring provides a reduction in frictional resis-tance between the ring and the cylinder wall, good sealing against gas blow-by and enhanced engine performance and exhaust emissions control.

Description

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 ~ :

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 , .

, 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

-4a-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 ,~ .. ,:,.;

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 ( 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 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 .,~ . .,.~. , ::
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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 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 '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--15- . ~

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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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--18- '~ , ~ .

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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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Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An annular piston ring for an internal combustion engine having an upper radial surface which defines the upper portion of the ring, a lower radial surface which defines the lower portion of 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 circumferentially 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 of the outside of the recessed outer face and the radius and said axial bearing surface being greater than the radial thick-ness of the hard facing alloy on the ring, and a circumferentially extending inner peripheral relief formed in the upper-inner portion of the ring said relief having an inside diameter greater than the inside diameter of the ring.

2. The piston ring of claim 1, wherein a circumferential groove is formed in the bearing surface and the hard facing alloy is disposed therein.

3. The ring of claim 1 wherein the lower radial surface is a substantially flat, ungrooved surface extending between the inner and outer axial surfaces.

4. The piston ring of claim 3 wherein the upper and lower radial surfaces of the ring are parallel to each other and perpendicular to the recessed outer face.

5. The ring of claim 1 wherein the outer radial ledge is perpendicular to the recessed outer face and the recessed outer face is parallel to the longitudinal axis of the ring.

6. The piston ring of claim 1 in a groove in a piston in an internal combustion engine and wherein the radially outwardly directed force created by gas pressure exerted on the inner axial surface of the ring is at least partially offset by a radially inwardly directed force created by gas pressure exerted on the recessed outer face of the ring, and wherein the radially inwardly directed force does not appreciably change during the life of the ring.