GB2117086A - Piston rings - Google Patents

Abstract

A piston ring has a wear-resistant band (38) disposed between two lands (40, 42). The piston ring is split, the division including two oppositely disposed surfaces (52, 70) which are radially and axially inclined and which terminate in one of the lands (40). This construction means that the wear-resistant band (38) terminates at axially extending edges (80, 62) but does not have exposed circumferentially extending edges, which would be prone to damage during manufacture. In one embodiment the band is nearer one edge of the ring than the other and the outer surface of the ring is barrelled assymetrically so that the widest part of the ring is in the centre of the band. <IMAGE>

Description

SPECIFICATION Piston rings This invention relates to piston rings.

It has heretofore been recognized that a split piston ring having a wear-resistant coating on its outer peripheral surface may be advantageously employed as a top or compression piston ring 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.

2,266,692 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. Examples of such seal joint designs are shown in U.S. Pat. No. 61 5,902 to Raworth.

However, it has been found that the overlap-type gap joints previously proposed to provide effective sealing cannot be utilized 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.

According to the present invention there is provided a piston ring having a circumferential band of wear-resistant material on its radially outer peripheral surface, the band being disposed between two axially spaced lands, the ring being circumferentially divided in a manner such that portions of the ring on opposite sides of the division axially overlie each other, these portions having respective oppositely disposed surfaces which meet the outer peripheral surface of the ring in one of the lands, the surfaces extending radially inwardly from that land and sloping towards a plane which is perpendicular to the axis of the ring and passes through the other land.

Piston rings in accordance with the present invention combine the advantageous characteristics of wear-coated piston rings with the improved blow-by sealing characteristics of overlapping-type joint designs, while the wearresistant coating extends completely circumferentially around the bearing surface of the ring.

For better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a top plan view of a piston ring; Figure 2 is a fragmentary vertical sectional view taken on the line 2-2 of Figure 1; Figure 3 is a fragmentary enlarged view of a partion of the ring illustrated in Figure 2; Figure 4 is a fragmentary vertical elevational view looking in a direction of the arrow A of Figure 1; Figure 5 is a fragmentary vertical sectional view taken on line 5-5 of Figure 1; Figure 6 is a fragmentary top plan view illustrating the parted ends of the ring in an exaggerated free state condition; Figure 7 is a bottom plan view similar to Figure 6; Figure 8 is a fragmentary persepective view of the parted ends of the top surface of the ring;; Figure 9 is a fragmentary perspective view illustrating the parted ends of the bottom surface of the ring; and Figure 10 is a fragmentary view, similar to Figure 3, of a portion of a other piston ring.

The piston ring 20 of Figure 1 is one exemplary presently preferred form for use as a top compression ring in a diesel engine. As best seen by comparing Figures 1 to 4, the 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 radius R (Figure 2). The cross sectional configuration of ring 20 is of the keystone type. i.e. 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.

As 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 unequal in width (measured axially of the ring 20). The radius R is centered upon 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 and 7 of the aforementioned Raworth U.S.

Pat. No. 615,902. Thus, 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 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 cylinder bore of an engine, tongue 50 underlies and slidably overlaps the opposite parted recessed end 54 of the 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 about a radius R' (Fig. 10), which, unlike the face 22 of the ring 20 shown in Fig. 3 whose 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 slightly 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 wearresistant material will be in contact with the cylinder wall of the engine at all times.

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 axially extending outer edge 62 of tongue 50, and the end face 64 of tongue 50 is disposed on a radial 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 circumferentially 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 outer edge of face 51 to end face 64 (Fig. 7) and an upper land extension 40b 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 two times the axial dimension of land extension 40b. It is also preferred that land extension 40b (Fig. 8) be at least equal to or slightly greater in axial dimension than lower land 42 of ring 20.Surfaces 52 and 70 (Figs. 5, 8 and 9) lie in planes at an acute angle with respect to plane P and extending generally diagonally of the ring body cross section.

In fabrication of the ring 20, after the angle seal joint is milled in the parted ends thereof, a plurality of such rings are fixtured on an arbor and plasmaspray 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 56 of extensions 40a and 40b are then located outside of the ring 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 chippage 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 ailows metal removal from surfaces 64 and 72 (and coating edges 62 and 80) without exceeding gap tolerances. In prior attempts to utilize an angle seal overlap joint in wear-coated rings 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 maintaining minimum clearance conditions between surfaces 52 and 70 to control gas leakage through the overlapped gap. Typically, in the exemplary rings heretofore mentioned, the clearance between these overlapping surfaces is maintained between the limits of 0.03 to 0.13 mm.

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 (Fig. 6) so as to be oriented in assembly in the direction 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 40 while still leaving land extensions 40a and 40b of sufficient width to insure edge strength. Nevertheless, and aithough 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 chromiumfilled rings, the principles of the invention are equally applicable to rings having other wear resistant materials filling the groove, such as molybdenum, ceramics, aluminum oxide, oxides of chromium, chromium carbide or titanium carbide.

In the foregoing description and the appended claims, directional terminology such as "top", "bottom", "upper" and"lower" 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 (14)

1. A piston ring having a circumferential band of wear-resistant material on its radially outer peripheral surface, the band being disposed between two axially spaced lands, the ring being circumferentially divided in a manner such that portions of the ring on opposite sides of the division axially overlie each other, these portions having respective oppositely disposed surfaces which meet the outer peripheral surface of the ring in one of the lands, the surfaces extending radially inwardly from that land and sloping towards a plane which is perpendicular to the axis of the ring and passes through the other land.

2. A piston ring as claimed in claim 1, in which the oppositely disposed surfaces are flat.

3. A piston ring as claimed in claim 1 or 2, in which the wear-resistant material is disposed in a groove which is defined between the lands and extends entirely around the outer peripheral surface of the ring.

4. A piston ring as claimed in any one of the preceding claims, in which the oppositely disposed surfaces, at their radially inner ends, meet the axial end face of the ring which is further from the said one land.

5. A piston ring as claimed in any one of the preceding claims, in which the band of wearresistant material terminates on opposite sides of the division at respective radially extending surfaces to provide axially extending end edges of the band, the oppositely disposed surfaces extending circumferentially from the radially extending surfaces.

6. A piston ring as claimed in any one of the preceding claims, in which the outer peripheral surface of the ring has a barrelled configuration, the region of maximum outside diameter of the outer peripheral surface being on the band of wear-resistant material.

7. A psiton ring as claimed in claim 6, in which the outer peripheral surface of the ring, as viewed in axial cross-section, is arcuate, the centre of the arc being disposed on the central plane of the ring.

8. A piston ring as claimed in claim 6, in which the outer peripheral surface of the ring, as viewed in axial cross-section, is arcuate, the centre of the arc being spaced from the central plane of the ring.

9. A piston ring as claimed in any one of claims 6 to 8, in which the region of maximum outside diameter of the outer peripheral surface is midway between the axial extremities of the band of wearresistant material.

10. A piston ring as claimed in any one of the preceding claims, in which one of the lands is axially wider than the other land.

11. A piston ring as claimed in claim 10, in which the land at which the oppositely disposed surfaces meet the outer periphery of the ring is the wider land.

12. A piston ring as claimed in claim 10, in which, in use of the piston ring in a reciprocating internal combustion engine, the wider land is disposed nearer the combustion chamber than the other land.

13. A piston ring as claimed in any one of the preceding claims, in which indicia are provided for indicating the intended oritientation of the ring in a piston ring groove.

14. A piston ring as claimed in any one of the preceding claims, in which the piston ring has a keystone cross-section.

1 5. A piston ring substantially as described herein with reference to, and as shown in, the accompanying drawings.