CA1264170A

CA1264170A - Piston ring

Info

Publication number: CA1264170A
Application number: CA000422445A
Authority: CA
Inventors: Dean S. Bunce
Original assignee: Dana Inc
Current assignee: Dana Inc
Priority date: 1982-03-12
Filing date: 1983-02-25
Publication date: 1990-01-02
Also published as: IT1166429B; AR230493A1; BR8301230A; IL67993A0; KR840004218A; GB8306621D0; DE3305920A1; ES281751Y; ES281751U; NL8300890A; GB2117086A; IT8347884A0; AU1206083A; JPS58166170A; SE8301332L; FR2523215A1; SE8301332D0; IN157220B

Abstract

ABSTRACT OF THE DISCLOSURE
A parted annular piston ring having an outer periphery for engaging a cylinder wall of an internal combustion engine is disclosed. A band of hard, wear-resistant material is secured in a groove which extends circumferentially completely around the outer periphery of the ring. The band is disposed axially between upper and lower narrow lands. An overlapping joint construction is provided at the parted ends of the ring and comprises mutually circumferentially overlappable surfaces inclined at an acute angle relative to the plane of the ring and terminating in the outer periphery of the ring along edges disposed in the upper land. The upper land is wider than the lower land, and the mutually overlappable joint surfaces terminate at their radially inward edges in the bottom side wall of the ring. The band has axially extending end edges exposed at the split, and the outer periphery of the ring has a barrel face contour such that the maximum outside diameter of the ring falls within the outer wear surface of the band.

Description

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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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A piston ring comprising a parted annular metal body having axial side walls for seating in a ring groove and an outer peripheral surface, the groove extending entirely around said outer peripheral surface and defined in part by axially spaced lands disposed on said surface, a band of wear-resistant material in said groove for sealing engagement with a cylinder wall, said lands being respectively adjacent opposing axially spaced edges of said band, said peripheral surface having an offset barrel face contour such that the maximum outside diameter of said ring falls upon the center of the axial dimension of said band, and an overlapping joint construction at the parted ends of the ring comprising opposed planar surfaces extending essentially diagonally of the ring body and inclined at an acute angle relative to the plane of said ring, said surfaces terminating at said outer peripheral surface within one of said lands, and the center of the axial dimension of said band being offset from the central plane of said ring body toward the ring side wall more remote from said one of said lands.

2. The piston ring set forth in claim 1 adapted to function as a compression ring for a piston in a recipro-cating piston engine and further comprising indicia for indicating installation orientation in a piston groove such that said one of said lands is disposed in the direction of the cylinder firing area.

3. The piston ring set forth in claim 2 wherein said planar surfaces of said joint terminate at their radially inward edges in the said side wall remote from said one of said lands.

4. The piston ring set forth in claim 3 wherein said surfaces of said joint extend circumferentially from an associated end wall defining one radial face of the ring gaps to another associated end wall defining the other radial face of the gaps, said groove extending circum-ferentially completely around said peripheral surface and said band having axially extending end edges exposed at the split.

5. The piston ring of claim 1, 2 or 4 wherein said ring has a keystone cross-sectional contour.

6. A piston ring for a reciprocating piston internal combustion engine comprising a parted annular metal body having an outer peripheral surface, a band of wear-resistant material extending entirely around said outer peripheral surface and adapted for sealing engagement with a cylinder wall, said band having a dimension axially of said ring which is less than that of said outer peripheral surface and being offset axially from the plane of said ring such that said outer peripheral surface includes land areas of unequal axial dimension integral with said body and disposed entirely around axially opposite edges of said band, said peripheral surface having an offset barrel face contour such that the maximum outside diameter of said ring falls upon the center of the axial dimension of said band, and an overlap joint construction at the parted ends of said ring comprising opposed planar surfaces extending diagonally of the ring cross section and terminating at said outer peripheral surface in the said land area of greater axial dimension.