Sealing ring assembly with wear stabilizing features

Abstract

A sealing ring assembly includes a ring segment that includes at least one feature configured to affect wear. The ring segment includes a sealing surface configured to seal against a bore, and one or more other surfaces configured to seal against other ring segments or a piston land. The at least one feature may include a feature extending radially outward from a base to the sealing surface, a recess such as a slot configured to open as the ring wears, a pocket configured to open as the ring wears, a hole configured to open to the sealing surface as the ring wears, or a combination thereof. The at least one feature may be radially tapered, axially tapered, or both. The sealing ring assembly is configured to be seated in a ring groove of a piston, and seal between a high-pressure region and a low-pressure region.

Description

Attorney Docket No. 000102-0044-W01SEALING RING ASSEMBLY WITH WEAR STABILIZING FEATURES

[0001] The present disclosure is directed to sealing ring assemblies having one or more features to affect ring wear.Cross-Reference to Related Application

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 697,190 filed September 20, 2024, the disclosure of which is hereby incorporated by reference herein in its entirety.Summary

[0003] In some embodiments, the present disclosure is directed to sealing ring assemblies, and their use in devices such as a linear generator. The sealing ring assemblies include features configured and arranged to affect ring wear characteristics. For example, by changing contact areas, pressurized areas, surface areas, recess size, or any other suitable geometric aspect, one or more ring segments of the sealing ring assembly may provide for improved wear characteristics. In some embodiments, features that induce uniform wear at all stages of life are incorporated into the design, to avoid the natural course of wear that may decrease the contact area with increasing wear, leading to higher contact pressure in a sealing segment. This can promote the runaway mechanism described above and results in uneven wear leading to seal failure. This disclosure presents details of design features on piston seals that induce uniform wear in the sealing ring assembly. These features ensure that regions of the seal wearing faster than others face greater resistance to further wear and enhance seal life.

[0004] In some embodiments, the present disclosure is directed to a ring segment having a first surface configured to seal against a bore of a cylinder, a second surface facing radially outward and arranged radially inward of the first surface, and at least one feature extending radially outward from a base coplanar with the second surface to the first surface. In some embodiments, the at least one feature includes a pedestal. In some embodiments, the at least one feature includes at least one of an axial taper or a radial taper. In some embodiments, the at least one feature includes at least three surfaces. In some embodiments, the second surface extends azimuthally towards opposite ends of the ring segment, the second surface isconfigured to interface to at least one other sealing ring segment, and the second surface is configured to be exposed to a low-pressure region of the bore. In some embodiments, the at least one feature includes a radially outward surface, and the radially outward surface includes a surface area lesser than an area of the base. In some embodiments, the ring segment has a radial thickness that extends from a radially inward surface to the first surface. In some such embodiments, the at least one feature includes a radially outward surface comprising an area, the radial thickness is configured to decrease as the ring segment wears against the bore, and the area is configured to increase as the as the ring segment wears against the bore. In some embodiments, the first surface has a first area, the at least one feature has a radially outward surface having a second area, and the at least one feature is configured to increase a summation of the first area and the second area as the ring segment wears against the bore. In some embodiments, the ring segment includes a third surface extending radially outward from the second surface to the first surface. In some such embodiments, the third surface is axially rearward facing and is configured to seal against a second ring segment. In some embodiments, the ring segment includes a pocket arranged at the third surface that is configured to receive gas from a high-pressure region of the bore. For example, the pocket is configured to open as the ring segment and the second ring segment wear against the bore.

[0005] In some embodiments, the present disclosure is directed to a sealing ring assembly having a first ring segment configured to seal against a bore and a second ring segment configured to seal against the second surface and against the bore. In some embodiments, the first ring segment includes a first surface configured to seal against the bore, a second surface facing radially outward and arranged radially inward of the first surface, and at least one feature extending radially outward from a base coplanar with the second surface to the first surface.

[0006] In some embodiments, the present disclosure is directed to a device that includes a cylinder having a bore, a piston configured to move along the bore and having a ring groove, and a sealing ring assembly arranged in the ring groove and configured to seal against the bore. In some such embodiments, the sealing ring assembly includes a first surface configured to seal against the bore, a second surface facing radially outward and arranged radially inward of the first surface, and at least one feature extending radially outward from a base coplanar with the second surface to the first surface.

[0007] In some embodiments, the present disclosure is directed to a ring segment havinga slot embedded in an axially rearward surface of the ring segment, and a radially outward surface of the ring segment is arranged to contact a bore of a cylinder. In some embodiments, the slot includes one or more of a tapered or curved profile such that as material of the axially outward surface wears, a contact surface area of the axially outward surface increases.

[0008] In some embodiments, the present disclosure is directed to a ring segment having a pocket embedded in a surface to contact another ring segment, and the pocket is in fluid communication with a pressurized region based on a feature coupling the pocket to the pressurized region. In some embodiments, an opening of the pocket increases in size when the surface to contact the different sealing ring segment wears, and an area of the surface of the sealing ring segment exposed the pressurized region receives a larger magnitude of pressurized gas based on an amount of wear of material comprising the surface.

[0009] In some embodiments, the present disclosure is directed to a ring segment having a pocket on a surface of the sealing ring segment arranged to contact a second surface of a different sealing ring segment. In some such embodiments, the pocket is in fluid communication with a pressurized region, and the pocket has a hangar geometry that increases surface area exposed to gas pressurization area as the surface wears.

[0010] In some embodiments, the present disclosure is directed to a ring segment having one or more slanted pressure saturation gas pockets embedded in a sealing surface of the ring segment. In some such embodiments, the one or more slanted pressure saturation gas pockets include one or more respective openings that each increase in respective length as the sealing surface wears.

[0011] In some embodiments, the present disclosure is directed to a ring segment having one or more blind holes arranged on a radially outer sealing surface to contact a bore of a cylinder. In some such embodiments, the openings of the one or more blind holes become exposed to the bore of the cylinder with wear of the radially outer sealing surface.

[0012] In some embodiments, the present disclosure is directed to a ring segment configured to seal between a high-pressure region and a low-pressure region. In some such embodiments, the ring segment includes a sealing surface configured to seal against a bore of a cylinder, and at least one opening in the sealing surface. For example, the at least one opening extends from the sealing surface to an adjacent axial surface exposed to the low- pressure region, and a radially outward cross-sectional area of the at one opening is greater than a radially inward cross section area of the at least one opening. In some embodiments, the at least one opening include a blind opening such as a blind hole or a slot, for example. In some such embodiments, the slot has one or more of a tapered or curved profile such that asmaterial of the axially outward surface wears, a contact surface area of the axially outward surface increases.

[0013] In some embodiments, the present disclosure is directed to a ring segment having a sealing surface configured to seal against a bore of a cylinder and at least one feature. The at least one feature includes a first surface configured to seal against the bore and increase in contact area during wear, and a second surface configured to be exposed to a low-pressure region of the bore and decrease in area during wear. In some embodiments, the ring segment includes an inner surface facing radially outward and arranged radially inward of the sealing surface. In some such embodiments, the at least one feature extends radially outward from a base coplanar with the inner surface to the sealing surface.

[0014] In some embodiments, the present disclosure is directed to a ring segment having a first surface configured to seal against a bore of a cylinder, wherein the first surface comprises a first area, and a recess arranged at the first surface. In some embodiments, the recess defines a second area, and the second area is configured to increase during wear of the ring segment. In some embodiments, the recess is configured to be exposed to a high- pressure gas of the bore, and the recess is configured to cause a contact pressure between the bore and the first surface to be decreased based on the high-pressure gas. In some embodiments, the ring segment includes a second surface arranged radially inward of the first surface, and the second surface is configured to be exposed to a high-pressure gas of the bore. In some embodiments, the recess is fluidly coupled to a third surface of the ring segment configured to contact a high- pressure region of the bore. In some embodiments, the ring segment includes a blind recess arranged along the third surface, and the blind recess forms an opening in the first surface to become exposed to the bore during wear. In some such embodiments, before wear, the blind recess is closed to the bore and is closed to the first surface. In some embodiments, the recess includes a first portion having a cross-sectional area that decreases in a radially outward direction, the second area corresponds to a radially outermost cross-sectional area of the cross-sectional area, and the recess has a second portion extending from a front surface of the ring segment to an axial face of the first portion of the recess.

[0015] In some embodiments, the present disclosure is directed to a ring segment having a first surface having a contact area configured to seal against a bore of a cylinder, and a recess arranged in the first surface. In some embodiments, the recess is open to a low-pressure region of the bore, the recess has a radially outer cross-sectional area configured to decrease during wear, and the recess is configured to cause the contact area to increase during wear.In some embodiments, the recess is a slot open to the bore and to an axially rearward surface of the ring segment.

[0016] In some embodiments, the present disclosure is directed to a ring segment having a first surface having a contact area configured to seal against a bore of a cylinder, a second surface configured to seal against another ring segment, and a recess arranged in the second surface. In some embodiments, the recess is open to a high-pressure region of the bore, and the recess has a radially outer cross-sectional area configured to increase during wear. In some embodiments, the recess includes a pocket having at least one slanted face, for example. In some embodiments, the recess has a cross-sectional area that decreases in a radially outward direction, and the radially outer cross-sectional area corresponds to a radially outermost cross-sectional area of the cross-sectional area. In some embodiments, the recess is open to the bore and open to an azimuthal surface of the ring segment. In some embodiments, the recess is initially arranged radially inward from the first surface such that the recess initially avoids contact with the bore, and after at least some radial wear, the recess opens to the first surface to contact the bore.

[0017] In some embodiments, the present disclosure is directed to a sealing ring assembly including any of the ring segments of the present disclosure, and a second ring segment configured to interface to the first ring segment. In some embodiments, the present disclosure is directed to a device that includes a cylinder having a bore, a piston configured to move along the bore and having a ring groove, and a sealing ring assembly that includes any of the ring segments of the present disclosure and a second ring segment configured to interface to the first ring segment. In some embodiments, the ring segment is configured for oil-less operation. In some embodiments, the ring segment includes a self-lubricating material. For example, in some embodiments, the ring segment is made of a graphite material.Brief Description of the Drawings

[0018] The present disclosure, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments. These drawings are provided to facilitate an understanding of the concepts disclosed herein and shall not be considered limiting of the breadth, scope, or applicability of these concepts. Itshould be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

[0019] FIG. 1A shows a cross-sectional view of a portion of an illustrative cylinder and piston assembly having a piston seal section with a wear stabilizing feature, and FIGS. 1B-1D show enlargements of sealing ring assemblies, in accordance with some embodiments of the present disclosure;

[0020] FIG. 2 shows a cross-sectional view of an illustrative device having two free-piston assemblies, in accordance with some embodiments of the present disclosure;

[0021] FIGS. 3A-3G show perspective views of an illustrative sealing ring assembly, or segments thereof, having wear stabilization features, in accordance with some embodiments of the present disclosure;

[0022] FIGS. 4A-4D show perspective views of an illustrative sealing ring assembly and segments thereof having another type of wear stabilization features, in accordance with some embodiments of the present disclosure;

[0023] FIGS. 5A-5B show top views of a portion of an illustrative sealing ring assembly and interfaces thereof at two stages of wear, in accordance with some embodiments of the present disclosure;

[0024] FIGS. 5C-5D show front views of the portions of FIGS. 5A-5B, in accordance with some embodiments of the present disclosure;

[0025] FIGS. 6A-6C show several views of an illustrative sealing ring assembly and segments thereof, having a gas pocket, in accordance with some embodiments of the present disclosure;

[0026] FIGS. 7A-7B show several views of an illustrative sealing ring assembly and segments thereof, having a gas pocket, in accordance with some embodiments of the present disclosure;

[0027] FIGS. 8A-8C show several views of an illustrative sealing ring assembly and segments thereof, having a gas pocket of hangar geometry in an inter-segment region, in accordance with some embodiments of the present disclosure;

[0028] FIGS. 9A-9B show two perspective views of a portion of an illustrative ring segment having a tapered groove, at two stages of wear, and FIG. 9C shows an illustrative cross-sectional view, in accordance with some embodiments of the present disclosure; and

[0029] FIGS. 10A-10B show two perspective views of a portion of an illustrative ring segment having one or more blind recesses, at two stages of wear, in accordance with some embodiments of the present disclosure.Detailed Description of the Drawings

[0030] While designing piston seals for applications with highly regulated emissions standards, solid lubricant seals (e.g., having self-lubricating material and configured for oilless operation) provide benefits compared to seals requiring liquid lubricants. For example, graphite is a common material used for this application as it has self-lubricating properties. Due to its brittle nature, the strain in graphite seals needs to be restricted as it wears during operation to avoid breakage due to high deformation of its worn shape. In some circumstances, rings can experience uneven wear due to various factors such as uneven loading or non-uniform surface profile in the cylinder in which the ring traverses. When one ring segment or portion thereof wears faster than others, it can compromise the seal life. This can happen through a “runaway” mechanism wherein non-uniform wear changes the shape of the ring in such a way that contact pressure in the fast-wearing region increases, further increasing the wear rate in the fast-wearing region, thus creating a positive feedback mechanism. If the fast-wearing runaway segment experiences higher contact pressure at the cylinder wall (i.e., the bore), it leads to even faster wear. For example, the resulting unevenly-worn shape of the ring may experience strain in excess of the material strength while conforming to the cylinder wall under pressure. Additionally, gaps may open in the sealing ring as a result of the uneven worn shape, resulting in loss of sealing efficiency.

[0031] This disclosure provides wear stability features for inclusion in sealing ring assemblies to induce uniform wear during operation (e.g., at all or most times), by inducing resistance to further wear in the fast-wearing components or regions. In some embodiments, contact pressure decreases with more wear, which may be accomplished via physical features on the sealing ring that expose more contact surface with further wear (Mode I), increase the surface area exposed to cylinder gas pressurization in the contact region (Mode II), or both.

[0032] In some embodiments, the present disclosure is directed to a sealing ring assembly for sealing against a bore that includes one or more ring segments. At least one ring segment includes an outer surface for sealing against the bore. The outer surface includes regions of contact, for example, that have corresponding surface areas and contact pressures during operation. The at least one ring segment also includes regions of high pressure (e.g., exposed to high-pressure gas) and regions of low pressure (e.g., exposed to low-pressure gas), along with regions of contact where the segment seals against the bore. During operation, the sealing surface (e.g., the contact surface against the bore) of the at least one ring segment isconfigured to wear down radially. During this wear, (i) the regions of low-pressure decrease in area, and (ii) either or both of the regions of high-pressure (e.g., applying gas pressure radially inward) and the regions of contact increase in area. Accordingly, as a ring segment wears, these dynamics provide wear stability (e.g., as segments wear faster the geometric change in regions tend to lessen or counteract the wear rate).

[0033] FIG. 1 A shows a cross-sectional view of a portion of illustrative cylinder and piston assembly 100 having a piston seal section with a wear stabilizing feature, in accordance with some embodiments of the present disclosure. As illustrated, piston and cylinder assembly 100 includes sealing ring assembly 120, cylinder 160 may include bore 162, which is the inner cylindrical surface in which piston assembly 110 travels. Piston assembly 110 includes piston 126, which includes sealing ring groove 122, in which sealing ring assembly 120 is configured to ride. As piston assembly 110 translates along axial direction (e.g., indicated by direction 180) during a stroke of a cycle, in cylinder 160, the gas pressure in high-pressure region 150 may change (high-pressure region 150 may be closed with a cylinder head or an opposing piston). For example, as piston assembly 110 moves to the left in FIG. 1 A, the pressure in high-pressure region may increase. Low pressure region 170, located to the rear of sealing ring assembly 120 may be at a gas pressure below the pressure of high-pressure region 150 for at least some, if not most, of a stroke or cycle of piston and cylinder assembly 100. The pressure ranges in high-pressure region 150 and low-pressure region 170 may be any suitable ranges (e.g., sub-atmospheric pressure to well over 250 bar), and may depend on compression ratio, breathing details (e.g., boost pressure, pressure waves, port timing), losses, thermochemical properties of gases, and reaction thereof. Accordingly, the sealing ring assemblies described herein may be used to seal any suitable high-pressure region and low- pressure region, having any suitable pressure ranges. For example, in some embodiments, low-pressure region 170 may interact flow- wise with intake or exhaust ducting, and be maintained relatively near pressure in the ducting. In an illustrative example, low-pressure region 170 may open to intake breathing ports, and may be at a pressure near to or strongly affected by (e.g., on average) an intake pressure (e.g., a boost pressure). In a further illustrative example, low-pressure region 170 may open to exhaust breathing ports, and may be at a pressure near to or strongly affected by (e.g., on average) an exhaust pressure. In accordance with the present disclosure, sealing ring assemblies may be used to seal high- pressure regions from low-pressure regions for at least part of a stroke or cycle of a piston and cylinder assembly. It will be understood that the "front" of sealing ring assembly 120refers to the face axially nearest high-pressure region 150, and the "rear" of sealing ring assembly 120 refers to the face axially nearest low-pressure region 170.

[0034] It will be understood that unless otherwise specified, all pressures referred to herein are in absolute units (e.g., not gage or relative). It will also be understood that high-pressure and low-pressure may refer to transient pressure states of a piston and cylinder device. For example, referencing a thermodynamic cycle, the high-pressure side of a sealing ring assembly may have a pressure greater than a low-pressure side of the sealing ring assembly for most of the engine cycle (e.g., except possibly during breathing or near-breathing portions of the cycle). Accordingly, high-pressure and low pressure are relative and depend on the conditions of the gas being sealed. For example, a sealing ring assembly may be used to seal a high pressure and a low-pressure region, each operating in any suitable pressure range. It will also be understood that a sealing ring assembly may seal differently at different positions in a cycle. It will be further understood that a low-pressure region may include a pressure greater than a pressure of a high-pressure region for some of a piston stroke or cycle of a piston and cylinder assembly. For example, a sealing ring assembly may always seal a high- pressure region from a low-pressure region. In a further example, a sealing ring assembly may seal a high-pressure region from a low-pressure region as long as the pressure in the high-pressure region is greater than the pressure in the low-pressure region. In a further example, a sealing ring assembly may seal a high-pressure region from a low-pressure region as long as the pressure in the high-pressure region is greater than the pressure in the low- pressure region, and conversely, seal a low-pressure region from a high-pressure region as long as the pressure in the low-pressure region is greater than the pressure in the high- pressure region.

[0035] In some embodiments, sealing ring assembly 120 may deposit material on bore 162 of cylinder 160 (e.g., include a self-lubricating material, which may include graphite). Deposited material may lubricate the bore-to-sealing ring assembly interface between bore 162 and sealing ring assembly 120 (e.g., provide a dry lubricant). Accordingly, in some embodiments, piston and cylinder assembly 100 may operate without liquid for lubrication (e.g., oil). In some embodiments, piston 126 may be an open-faced piston. For example, piston 126 may include openings, cutouts, or other fluid paths from high-pressure region 150 to ring groove 122. Accordingly, in some embodiments employing an open-faced piston, the radially inward surfaces (e.g., referencing radial direction 182 in FIG. 1A) of sealing ring assembly 120 may be exposed to gas pressure of high-pressure region 150.

[0036] FIG. IB shows an enlargement of region 101 of FIG. 1 A, in accordance with some embodiments of the present disclosure. As illustrated, sealing ring assembly 120 includes ring segment 129, which is configured to seal against land 111 and bore 162. For example, as illustrated, sealing ring assembly 120 may include feature 121 (e.g., illustrated as a recess but may include any of the illustrative features of the present disclosure) for providing wear stability. As illustrated, feature 121 is configured to form low-pressure region 125 (e.g., bounded by feature 121, bore 162, and piston land 111. Low-pressure region 125 may be filed with gas from, or otherwise correspond to, low-pressure region 170 (e.g., gas from low- pressure region 170 may fill or otherwise affect gas pressure in low-pressure region 125). During wear, as ring segment 129 wears against bore 162 at contact area 123 (e.g., a region of contact with a corresponding contact pressure), ring segment 129 may move outward along radial direction 182 as material wears at contact area 123 (e.g., of a radially outward sealing surface), which experiences contact / gas pressure 152 (e.g., a contact pressure between contact area 123 of sealing ring assembly 120 and bore 162, and gas pressure caused by recess 131 fed from high-pressure region 150). For example, during operation gas pressure 151 may be caused by high-pressure region 150 (e.g., may be the same as or nearly the same as a gas pressure of high-pressure region 150). Contact / gas pressure 152 may be caused by bore 162 pressing against contact area 123 along with gas pressure from gas in recess 131. For example, during operation, a radial force balance at zero radial acceleration may be represented as:F outward F inward(gas pressure 151)*(area 124) = (contact pressure)* (contact area 123)+(gas pressure)*(gas area) where gas pressure 151 corresponds to pressure from gas of high-pressure region 150, area 124 corresponds to a radially inward surface of ring segment 129, the contact pressure (e.g., of contact / gas pressure 152) acts on contact area 123, and the gas pressure (e.g., of contact / gas pressure 152) acts on an area of pressurized gas caused by recess 131 (e.g., the area may be the same as or slightly larger than the cross-sectional area of recess 131 at bore 162). Note that contact area 123 corresponds to an area of a radially outer surface of ring segment 129, minus the area of pressurized gas caused by recess 131. Accordingly, for a given left-hand side (LHS) of the above expression, greater contact area and / or greater gas pressure at the sealing surface correspond to a lessened contact pressure, which maycorrespond to a lessened wear. For example, for a given force in the outward radial direction due to the high-pressure gas acting on the radially inside surface (e.g., having corresponding area 124) of ring segment 120 and a given gas pressure at the sealing surface, the contact pressure at contact area 123 (e.g., of an outside diameter or otherwise radially outward sealing surface) may decrease with an increase in the area of the region of contact (e.g., contact area 123). As illustrated, contact area 123 abuts area 126, such that as area 126 decreases, contact area 123 increases. To illustrate, due to the slope, taper, volume, crosssection, or other suitable geometric property of the wear stabilization feature, with increasing wear, the contact area increases, contact pressure decreases, and the wear rate decreases. Thus, a negative feedback loop for wear stability may be achieved.

[0037] In an illustrative example, based on Archard’s wear equation, wear depth on a surface sliding against a counter surface is represented by the relationship between the variables in the following equation: w = K*contact pressure* sliding distanceIn the above equation, wear (“w”) is quantified based on a product of the constant K (e.g., a proportionality constant dependent on material properties and operating environment), contact pressure (e.g., between a sealing surface of a sealing ring segment and a bore of a cylinder), and a sliding distance along which the contact pressure is applied. Hence, for two different designs of a sealing segment running through the same sliding distance (or running for the same time at the same frequency), the one with higher contact pressure at the cylinder wall will generally wear faster. Archard’s equation may apply to sealing ring assembly 120, wherein contact area 123 wears against bore 162 at contact / gas pressure 152.

[0038] FIG. 1C shows the enlargement of region 101 at a later stage of wear as compared to FIG. IB, in accordance with some embodiments of the present disclosure. During operation, ring segment 129 may be configured to decrease a region corresponding to low pressure (e.g., low-pressure region 125) such that area 126 decreases. Area 126 corresponds to the open area of low-pressure region 125 as projected onto bore 162 (e.g., as extending azimuthally around ring segment 129). During operation, ring segment 129 may wear to result in ring segment 129C, having decreased low-pressure region 125C, with lesser area 126C (e.g., as compared to area 126). Further, the contact pressure of contact / gas pressure 152C may be lessened as compared to the contact pressure corresponding to contact / gas pressure 152 because contact area 123C is increased as compared to contact area 123. Note that area 124 and the gas pressure trace of high-pressure region 150 (e.g., over a stroke or cycle) may, butneed not, change appreciably during operation (e.g., over many cycles). Additionally, in some embodiments, recess 131 may be configured increase in cross-section area (e.g., gas area) with wear such that the product of gas pressure and the gas area increases with wear to further decrease contact pressure and thus wear.

[0039] FIG. ID shows an enlargement of region 101 of FIG. 1 A, in accordance with some embodiments of the present disclosure. As illustrated, sealing ring assembly 120 may include ring segment 139, which is configured to seal against land 111 and bore 162. As illustrated, ring segment 139 may include feature 131 (e.g., illustrated as a recess similar to recess 121 but may include any of the illustrative features of the present disclosure) for providing wear stability. As illustrated, feature 131 is configured to form low pressure region 135 (e.g., bounded by feature 131, bore 162, and piston land 111. Low-pressure region 135 may be filed with gas from, or otherwise correspond to, low-pressure region 170 (e.g., gas from low- pressure region 170 may fill or otherwise affect gas pressure in low-pressure region 135). During wear, as ring segment 139 wears against bore 162 at contact area 133 (e.g., a region of contact with a corresponding contact pressure), ring segment 139 may move outward along radial direction 182 as material wears at contact area 133 (e.g., of a radially outward sealing surface), which experiences contact / gas pressure 152 (e.g., including a contact pressure between contact area 133 of ring segment 139 and bore 162. For example, during operation gas pressure 151 may be caused by high-pressure region 150 (e.g., may be the same as or nearly the same as a gas pressure of high-pressure region 150). Contact pressure 153 may be caused by bore 162 pressing against contact area 133. For example, during operation, a radial force balance at zero radial acceleration may be represented as:F outward F inward(gas pressure 151)*(area 124) = (contact pressure)*(contact area 123) where gas pressure 151 corresponds to pressure from gas of high-pressure region 150, area 134 corresponds to a radially inward surface of ring segment 139, and the contact pressure (e.g., of contact / gas pressure 152) acts on contact area 133. Note that contact area 133 corresponds to an area of a radially outer surface of ring segment 139. Accordingly, for a given left-hand side (LHS) of the above expression, greater contact area at the sealing surface corresponds to a lessened contact pressure, which may correspond to a lessened wear. For example, for a given force in the outward radial direction due to the high-pressure gas acting on the radially inside surface (e.g., having corresponding area 134) of ring segment 120, thecontact pressure at contact area 133 (e.g., of an outside diameter or otherwise radially outward sealing surface) may decrease with the area of the region of contact (e.g., contact area 133). As illustrated, contact area 133 abuts area 136, such that as area 136 decreases, contact area 133 increases. To illustrate, due to the slope, taper, volume, cross-section, or other suitable geometric property of the wear stabilization feature, with increasing wear, the contact area increases, contact pressure decreases, and the wear rate decreases. Thus, a negative feedback loop for wear stability may be achieved.

[0040] FIG. 2 shows a cross-sectional view of illustrative device 200 having two firee- piston assemblies 210 and 220 (also referred to as translators herein), in accordance with some embodiments of the present disclosure. To illustrate, device 200 may be a linear generator configured to generate electric power based on a fuel input. To illustrate, any or all of sealing ring assemblies 212, 222, 281, and 286 may include any suitable sealing ring assembly architecture such as sealing ring assembly 120 of FIG. 1A, or any other sealing ring assembly of the present disclosure, for example.

[0041] In some embodiments, device 200 may include linear electromagnetic machines 250 and 255 to convert between kinetic energy of respective free piston assemblies 210 and 220 and electrical energy. In some embodiments, device 200 may include gas regions 260 and 262, which may, for example, be at a relatively lower pressure than gas region 270 (e.g., a high-pressure region) for at least some, if not most, of a cycle (e.g., a power cycle, or an air compression cycle). For example, gas regions 260 and 262 (e.g., low-pressure regions) may be open to respective breathing ducting (e.g., an intake manifold, an intake system, an exhaust manifold, an exhaust system). To illustrate, breathing ports 234 and 235 are configured to provide reactants to, and remove exhaust from, bore 232 of cylinder 230. In a further example, gas regions 260 and 262 may be vented to atmosphere (e.g., be at about 1.01 bar absolute pressure). In some embodiments, device 200 may include gas springs 280 and 285, which may be used to store and release energy during a cycle in the form of compressed gas (e.g., a driver section). For example, free piston assemblies 210 and 220 may each include respective pistons 282 and 287, having grooves for respective sealing ring assemblies 281 and 286, to seal respective gas regions 283 and 288 (e.g., high-pressure regions) from respective gas regions 284 and 289 (e.g., low-pressure regions).

[0042] Cylinder 230 may include bore 232, centered about axis 272. In some embodiments, free piston assemblies 210 and 220 may translate along axis 272, within bore 232, allowing gas region 270 to compress and expand. For example, gas region 270 may be at relatively high pressure as compared to gas region 260 for at least some of a stroke of freepiston assemblies 210 and 220 (e.g., which may translate along axis 272 in opposed piston synchronization). Sealing ring assemblies 212 and 222 may seal gas region 270 from respective gas regions 260 and 262 within bore 232. In some embodiments, free piston assemblies 210 and 220 may include respective pistons 214 and 224, and respective sealing ring assemblies 212 and 222 which may be arranged in respective corresponding grooves of pistons 214 and 224. It will be understood that gas regions 260 and 262, and gas region 270, may change volume as free piston assemblies 210 and 220 move or are otherwise positioned at different locations along axis 272. The portions of respective sealing ring assemblies 212 and 222 nearest gas region 270 are each termed the front, and the portion of sealing ring assemblies 212 and 222 nearest respective gas regions 260 and 262 are each termed the rear. Sealing ring assemblies 212 and 222 may each include a high-pressure boundary, which may each depend on a pressure in gas region 270. For example, a high-pressure boundary of sealing ring assembly 212 may be open to gas region 270 (e.g., coupled by one or more orifices, or other opening), and have a corresponding pressure the same as (e.g., if gas from gas region 270 is unthrottled in the sealing ring assembly), or less than (e.g., if gas from gas region 270 is throttled in the sealing ring assembly), the pressure of gas region 270. Sealing ring assemblies 212 and 222 may each include a low-pressure boundary, which may depend on a gas pressure in respective gas regions 260 and 262. For example, a low-pressure boundary of sealing ring assembly 212 may be open to gas region 260 and have a corresponding pressure about the same as the pressure of gas region 260.

[0043] In some embodiments, pistons 214 and 224 may each include one or more grooves into which one or more respective sealing ring assemblies may be arranged. For example, as shown in FIG. 2, pistons 214 and 224 may each include one groove, into which sealing ring assembly 212 and sealing ring assembly 222 may be installed, respectively. In a further example, although not shown in FIG. 21, piston 214 may include two grooves, in which two respective sealing ring assemblies may be installed. In a further example, piston 214 may include two grooves, the first sealing ring assembly 212, and the second (not shown), arranged to the rear of sealing ring assembly 212, but with its front nearer to gas region 260, thereby sealing pressure in gas region 260 to pressure between the two sealing ring assemblies (e.g., which may be less than pressure in gas region 270). Accordingly, a sealing ring assembly may be used to seal any suitable high pressure and low-pressure regions from each other.

[0044] In some embodiments, free piston assemblies 210 and 220 may include respective magnet sections 251 and 256, which interact with respective stators 252 and 257 to formrespective linear electromagnetic machines 250 and 255. For example, as free piston assembly 210 translates along axis 272 (e.g., during a stroke of an engine cycle), magnet section 251 may induce current in windings of stator 252. Further, current may be supplied to respective phase windings of stator 252 to generate an electromagnetic force on free piston assembly 210 (e.g., to effect motion of free piston assembly 210).

[0045] In some embodiments, pistons 214 and 224, sealing ring assemblies 212 and 222, and cylinder 230 may be considered a piston and cylinder assembly. In some embodiments, device 200 may be an engine, an air compressor, any other suitable device having a piston and cylinder assembly, or any combination thereof. In some embodiments, device 200 need not include two free piston assemblies. For example, cylinder 230 could be closed (e.g., with a cylinder head), and free piston assembly 210 alone may translate along axis 272.

[0046] FIGS. 3 A-3G show perspective views of illustrative sealing ring assembly 300, or segments thereof, having wear stabilization features, in accordance with some embodiments of the present disclosure. As illustrated in FIG. 3 A, sealing ring assembly 300 includes ring segments 310, 320, 330, 340, 350, 360, 370, and 380. For example, ring segments 310, 320, 330, and 340 are of a first type (e.g., similar to each other), and ring segments 350, 360, 370, and 380 are of a second type (e.g., similar to each other). While sealing ring assembly 300 is illustrated as having eight segments in total, with four segments of each type, a sealing ring assembly may include any suitable number and types of segments in accordance with the present disclosure. For example, a sealing ring assembly may include one ring segment of each type, or N segments of each type where N is a suitable positive integer greater than one. Axial direction 303, radial direction 302, and azimuthal direction 304 are illustrated in FIGS. 3A and 3G.

[0047] FIGS. 3B-3D show ring segment 310 at three successive states of wear, indicated by ring segment 310B (e.g., least worn), ring segment 310C (e.g., intermediately worn), and ring segment 310D (e.g., most worn). It will be understood that ring segment 310, as unworn, may assume any of the shapes and characteristics of ring segments 310B, 310C, or 310D, and be configured to wear such that the contact area 319 (e.g., of feature 316 against a bore) increases. As illustrated, ring segment 310B includes feature 316 arranged azimuthally between surfaces 311 and 312 (e.g., radially outward facing surfaces), surface 313 (e.g., a radially outward surface configured to seal against and contact bore 162), axial-facing surfaces 314 and 315 on either side of feature 316 (e.g., against which respective ring segments 350 and 360 seal), and axial-facing surface 317 (e.g., which may be configured to seal against piston land 111). Feature 316 of ring segment 310 is labeled, and it will beunderstood that ring segments 320, 330, and 340 also include similar respective features as feature 316. For example, ring segments 310B, 310C, and 310D may represent one of four similarly shaped segments, as worn over time. Contact area 319 may be zero, or otherwise an initial value, when ring segment 31 OB is at a low to no wear condition. As sealing ring assembly 300 wears, ring segment 310B may wear to result in ring segment 310C, wherein contact area 319 is increased (e.g., or forms and then is increased), surface 313 has worn radially such that segment 310C is radially less thick than ring segment 310B (e.g., surfaces 314 and 315 are reduced in area), and feature 316 has decreased in radial dimension. As sealing ring assembly 300 wears further, ring segment 310C may wear to result in ring segment 310D, wherein contact area 319 is further increased, surface 313 (e.g., also having a contact area) has further worn radially such that segment 310D is radially less thick than ring segment 310C (e.g., surfaces 314 and 315 are further reduced in area), and feature 316 has further decreased in radial dimension.

[0048] FIGS. 3E-3F show two perspective views of ring segment 310 and ring segment 360 (e.g., roughly indicated by region 301 in FIG. 3A). As illustrated, ring segment 360 is configured to seal against surface 312 and surface 315. Also, as illustrated, end 361 of ring segment 360 is spaced by distance 390 from feature 316. Distance 390 may increase as sealing ring assembly 300 wears against the bore. In a further example, as sealing ring assembly 300 wears, ring segment 360 may become radially thinner (e.g., along with surface 315), while maintaining a seal against surfaces 312 and 315. The same wear dynamics may occur for each combination A:B of interfacing ring segments A: {310, 320, 330, 340} and B:{350, 360, 370, 380}. For example, each ring segment may interface to (e.g., seal against) two other ring segments, or otherwise two ends of a single ring segment (e.g., if the ring includes only a total of two ring segments).

[0049] In some embodiments, for example, a wear stabilization feature such as feature 316 includes a protrusion arranged on a sealing segment (e.g., ring segment 310) in contact with the cylinder bore that increases the contact area (e.g., area 319) with wear. The protrusion (e.g., a wedge or pedestal) can be shaped such that it introduces more contact area in radial, azimuthal, and axial directions. FIGS. 3A-3G show an example of such illustrative features having such a pedestal geometry. As illustrated and labeled in FIG. 3G, segment 310 may be formed by tapered cuts in two directions (e.g., radial direction 302 and axial direction 303) to ensure that contact area 319 increases as ring segment 310 wears. For example, feature 316 includes surface 395 that tapers along axial direction 303, surface 397 that tapers along radial direction 302, and surface 396 that tapers along radial direction 302 and axial direction 303(e.g., at least during a portion of wear until contact area 319 merges with surface 397) has a tapered surface in the azimuthal plane and tapered surfaces in the axial plane, as shown below. As illustrated, feature 316 includes a pedestal having a base of dimensions length 391 and width 395, at the region where feature 316 meets surfaces 311 and 312 (e.g., which would form a single, radially outward-facing surface if feature 316 were removed). Further, as illustrated, feature 316 extends radially distance 393 away from the base, and tapers in two dimensions along radial distance 393. During wear, for example, length 391 and width 392 may remain constant, while distance 393 may decrease as surfaces 396, 395, and 397 decrease in area. In some embodiments, surface 395 need not taper (e.g., may extend in the radial direction such that feature 316 exhibits an azimuthal thickness of distance 391 along its radial length (e.g., distance 393). Any or all of surfaces 396, 395, and 397 may be tuned in shape and orientation (e.g., taper angle or otherwise surface contour) to affect wear rate during the course of ring wear.

[0050] In an illustrative example, a sealing ring may include a sealing ring segment having at least one protruding feature such as feature 316 extending from a sealing surface (e.g., surfaces 311 and 312) of the sealing ring segment, in which the sealing surface is exposed to a low-pressure during operation. To illustrate, the at least one protruding feature includes at least one pedestal. In some embodiments, the at least one protruding feature includes an axial taper, a radial taper, or both such that an end of the protruding feature (e.g., at contact area 319) is narrower than a base of the protruding feature. In some embodiments, an area of the feature exposed to low-pressure region 170 may increase with wear. For example, an area of surface 396 projected to bore 162 (e.g., illustrated by area 305 in FIG. 3G) may be configured to be exposed to low-pressure region 170 and decrease in area with increased wear. In some embodiments, surface 317 may include a contact surface that seals against land 111 but is not appreciably affected by low-pressure region 170. Area 305 may be arranged adjacent to contact area 319 during wear, extending axially rearward from contact area 319, for example.

[0051] In some embodiments, wear stabilization may be achieved using a recess feature open to a low-pressure region. For example, the recess may be produced by forming (e.g., machining, molding, casting, or otherwise suitably forming) a slot at the low-pressure end of the sealing ring. With increasing wear, the contract area in contact with the cylinder wall increases and reduces the area of the low-pressure region. The results is a reduction of contact pressure with wear.

[0052] FIGS. 4A-4D show perspective views of illustrative sealing ring assembly 400 and segments thereof having another type of wear stabilization feature, in accordance with someembodiments of the present disclosure. As illustrated in FIG. 4A, sealing ring assembly 400 includes ring segments 410, 420, 430, 440, 450, 460, 470, and 480. For example, ring segments 410, 420, 430, and 440 are of a first type (e.g., similar to each other), and ring segments 450, 460, 470, and 480 are of a second type (e.g., similar to each other). While sealing ring assembly 400 is illustrated as having eight segments in total, with four segments of each type, a sealing ring assembly may include any suitable number and types of segments in accordance with the present disclosure. For example, a sealing ring assembly may include one ring segment of each type, or N segments of each type where N is a suitable positive integer greater than one. Axial direction 403, radial direction 402, and azimuthal direction 404 are illustrated in FIG. 4A.

[0053] FIGS. 4B-4C show perspective views of ring segments 410 and 460 at two successive states of wear, indicated by enlargement 401 (e.g., least worn) and enlargement 401C (e.g., most worn). It will be understood that ring segments 410 and 460, as unworn, may assume any of the shapes and characteristics of enlargements 401 or 401C, and be configured to wear such that the contact area of surface 463 increases (e.g., as feature 461 lessens in size). As illustrated, ring segment 460 includes feature 461 arranged azimuthally along surface 463 and surface 466 (e.g., arranged at a radially outward intersection of the surfaces), where surface 463 is configured to seal against, and wear against, the bore. For example, surface 413 of ring segment 410 (e.g., a radially outward surface configured to seal against bore 162), and surface 463 may form a seal against the bore. As illustrated, ring segment 410 includes axial-facing surface 414 (e.g., against which respective ring segments 450 and 460 seal), axial -facing surface 417 (e.g., which may be configured to seal against piston land 111), and radially outward-facing surface 411 configured to seal against ring segment 460 (e.g., against a radially inward surface of ring segment 460). To illustrate, a surface of ring segment 460 similar to surface 488 of ring segment 480 may be configured to seal against surface 414, and a surface of ring segment 460 similar to surface 487 of ring segment 480 may be configured to seal against surface 411. The same wear dynamics may occur for each combination A:B of interfacing ring segments A: {410, 420, 430, 440} and B:{450, 460, 470, 480}. For example, each ring segment may interface to (e.g., seal against) two other ring segments, or otherwise two ends of a single ring segment (e.g., if the ring includes only a total of two ring segments). For example, enlargements 401 and 401C may represent one set of interfacing ring segments (e.g., sealing ring assembly 400 includes eight interfaces, as illustrated), as worn over time, with enlargement 401C worn more than enlargement 401. Referencing FIG. 4B, surface 463 may include a first surface areaconfigured to seal against the bore as a contact surface (e.g., an initial value, when ring segment 460 is at a low to no wear condition). As sealing ring assembly 400 wears, ring segments 410 and 460 of FIG. 4B may wear to result in the configuration illustrated in FIG. 4C, wherein the contact area of surface 463 is increased with wear, and surface 413 has worn radially, such that ring segments 410 and 460 are radially less thick in FIG. 4C than FIG. 4B (e.g., surface 414 is reduced in area), and feature 461 has decreased along radial direction 402.

[0054] Feature 461 of ring segment 460 is labeled, and it will be understood that ring segments 450, 470, and 480 also include similar respective features as feature 461. Feature 461, as illustrated in FIG. 4D, includes a recess (e.g., a slot), extending into surface 463 a distance 491. Feature 461 has a cross-section formed by distances 490 and 492 that corresponds to a recess of surface 463. During wear, feature 461, illustrated as a blind recess, becomes shallower (e.g., distance 491 lessens) and corresponds to a decreasing decrement of surface 463 (e.g., cross-section of distances 490 and 492 lessens). To illustrate, during wear, the contact area of surface 463 may increase as recess 461 lessens in size (e.g., in crosssection). Because feature 461 includes a cross-section that acts as a pocket or cutout of surface 463, the area of surface 463 may increase as a cross-section of recess 461 decreases. As illustrated, feature 461 is arranged in surface 463, and may also extend through surface 466 (e.g., be arranged at an intersection of surfaces 463 and 466). For example, feature 461 may include a recess volume defined by distances 490-494 and the shape of surfaces extending along distances 490-494, as illustrated by enlargement 405 in FIG. 4D. In a further example, as illustrated, feature 461 is tapered along radial direction 402 (e.g., distance 490 is greater than distance 494). In some embodiments, feature 461 is tapered along azimuthal direction 404 (e.g., distance 492 may change along azimuthal direction 404). In some embodiments, feature 461 is tapered along axial direction 403 (e.g., distances 490 and 494 may change along axial direction 403). For example, distance 492 need not taper uniformly in any direction.

[0055] In some embodiments, for example, a wear stabilization feature such as feature 461 includes a recess (e.g., a slot) arranged on a sealing segment (e.g., ring segment 460) in contact with the cylinder bore that increases the contact area with wear. The recess (e.g., a slot, hole, or otherwise pocket) can be shaped such that it represents lessened cross-sectional area in the azimuthal and axial directions 403 and 404 with wear. FIGS. 4A-4D show an example of such illustrative features having such a recess geometry. Because the cross- sectional area of feature 461 decreases with wear, for a given force directed radially outward,the contact area of surface 463 increases and thus the contract pressure decreases at surface 463.

[0056] In an illustrative example, a sealing ring may include a sealing ring segment having at least one recess feature such as feature 461 extending from at least one sealing surface (e.g., surfaces 466 and 463) of the sealing ring segment, in which the feature is exposed to a low-pressure region during operation. To illustrate, the at least one recess feature includes at least one slot. In some embodiments, the at least one recess feature includes a taper such that a blind end of the recess feature is narrower than an open end of the recess feature (e.g., along radial direction 402).

[0057] In another illustrative example, a sealing ring may include a sealing ring segment having at least one slot embedded in an axially rearward surface of the sealing ring segment. The radially outward surface is arranged to contact a bore of a cylinder, for example. In some embodiments, the at least one slot includes one or more of a tapered or curved profile such that as material of the radially outward surface wears, a contact surface area of the radially outward surface (e.g., surface 463, which does not include a cross section of dimension distance 490 by distance 492) increases.

[0058] FIGS. 5A-5B show top views of a portion of illustrative sealing ring assembly 500 and 500B, and interfaces thereof, at two stages of wear, in accordance with some embodiments of the present disclosure. FIGS. 5C-5D show front views of the portions of FIGS. 5A-5B, in accordance with some embodiments of the present disclosure. Accordingly, FIGS. 5A and 5C correspond to a less-worn or unworn state, and FIGS. 5B and 5D correspond to a more-worn state. As illustrated, sealing ring assembly 500 includes ring segment 510 and ring segment 520, which interface with each other. It will be understood that sealing ring assembly 500 may include any suitable number ring segments. For example, sealing ring assembly may include 2N ring segments into total, with N segments similar to ring segment 510 and another N segments similar to ring segment 520 (e.g., arranged in an alternating manner), wherein N may be any suitable positive integer (e.g., one or greater than one). Accordingly, for 2N ring segments, the sealing ring assembly may include 2N interfaces between adjacent segments (e.g., in FIGS. 3A-4D, N is illustratively equal to 4).

[0059] As illustrated, ring segment 510 includes feature 511, which is a wear stabilizing feature that is configured to increase a gas pressurization area on a radially outward sealing surface as sealing ring assembly 500 wears. The radially outward sealing surface includes surface 515 of ring segment 510 and surface 525 of ring segment 520, along with corresponding suitable surfaces of other suitable ring segments that may be included. Asillustrated, a feature such as feature 511 may include a tapered recess forming a slanted, intersegment pocket that increases the region exposed to gas pressurization as the ring wears. As illustrated, feature 511 includes a radial depth of distance 594, a radially outward open length of distance 591, a radially inward open length of distance 593, and an axial thickness of distance 590. The area open to a high-pressure region (e.g., high-pressure region 150 of FIG. 1 A) at the radially outward boundary is defined by distance 590 and distance 591 (e.g., the product of the distances, defining an area at the ring-bore interface).

[0060] In an illustrative example, feature 511 forms a slanted, inter-segment pocket that is configured to be filled with high-pressure gas (e.g., from high-pressure region 150). As the pocket “opens up” with wear (e.g., as distance 594 decreases), distance 591 in the azimuthal direction increases. As the region along slant 518 wears, a larger area (e.g., equivalent to the area defined by distance 590 and distance 591) of high-pressure gas is exposed to surface 519, resulting in an increased force in the inward radial direction (e.g., at surface 519), thus decreasing the contact pressure of ring segment 510 against the cylinder wall (i.e., bore 162). The contact pressure is lowered due to reduced net overall outward gas pressure on the segments in the radial direction since a portion of the pressure caused by the high-pressure gas pushing the ring radially outward gets compensated by (e.g., countered by) gas filling on the volume of feature 511. In some embodiments, feature 511 may include a slanted pocket (e.g., a pocket having at least one slanted face). In some embodiments, feature 511 is open to azimuthal face 530 of ring segment 510.

[0061] The length of the exposed region LI (e.g., which may correspond to distance 591, which increases with wear) is smaller at a lower wear life and creates less back pressure on the ring segment as compared to the worn ring. This is because the overhang region along slant 518, while pressurized the same as the rest of the cavity, exerts only internal forces on the segment, leaving a smaller length LI of open area to apply pressure on the cylinder (e.g., cylinder 160, with bore 162) and ring segment 510. The further worn state of ring segment 510 illustrated in FIGS. 5B and 5D has a smaller overhang region and larger open length L2 (e.g., corresponding to distance 591 at a greater wear state) that applies pressure over a larger area thus resulting in a larger radial force on the ring segment. The larger area associated with L2 as compared to LI is illustrated by the arrows indicating pressure acting over the respective areas.

[0062] In an illustrative example, adjoining sealing segments may use inter-ring gas pockets to reduce friction by allowing pressurized gas (e.g., from high-pressure 150) fill in these recesses. Such recesses, having suitable volumes and dimensions, can also be used toreduce contact pressure on the radially outward sealing surface (e.g., surfaces 515 and 525). When exposed to the radially outward sealing surface, high-pressure gas filling the volume of feature 511 creates gas pockets that reduce the net radially outward forces on sealing segments. These forces act to oppose the pressure forcing the ring radially outward.

[0063] FIGS. 6A-6C show several views of illustrative sealing ring assembly 600 and segments thereof, having a gas pocket, in accordance with some embodiments of the present disclosure. To illustrate, sealing ring assembly 500 of FIGS. 5A-5D may be the same as, similar to, or otherwise included as part of, sealing ring assembly 600. Axial direction 603, radial direction 602, and azimuthal direction 604 are illustrated in FIG. 6A. As illustrated in FIG. 6A, sealing ring assembly 600 includes ring segments 610, 620, 630, 640, 650, 660, and 670-675. For example, ring segments 610, 620, 630, 640, 650, and 660 are of a first type (e.g., similar to each other), and ring segments 670, 671, 672, 673, 674, and 675 are of a second type (e.g., similar to each other). While sealing ring assembly 600 is illustrated as having twelve segments in total, with six segments of each type, a sealing ring assembly may include any suitable number and types of segments in accordance with the present disclosure. For example, a sealing ring assembly may include one ring segment of each type, or N segments of each type where N is a suitable positive integer greater than one.

[0064] FIGS. 6B-6C show perspective views of ring segments 610 and 670 at two successive states of wear, indicated by enlargement 601 (e.g., least worn) and enlargement 601C (e.g., most worn). It will be understood that ring segments 610 and 670, as unworn, may assume any of the shapes and characteristics of enlargements 601 or 601C, and be configured to wear such that feature 611 opens with wear (e.g., as a radially outward area of feature 611 increases in size). As illustrated, ring segment 610 includes feature 611 arranged azimuthally along surface 613 and configured to seal against, and wear against, the bore. Ring segment 670 includes surface 683 configured to wear against the bore. Additionally, ring segment 610 includes surface 614, which is axially facing and configured to seal against surface 678 of ring segment 670 (e.g., surface 678 is similar to surface 688 of ring segment 673, facing forward along axial direction 603). For example, surface 613 of ring segment 610 (e.g., a radially outward surface configured to seal against bore 162), and surface 683 may form a seal against the bore. The same wear dynamics may occur for each combination A:B of interfacing ring segments A:{610, 620, 630, 640, 650, 660} and B:{670, 671, 672, 673, 674, 675}. For example, each ring segment may interface to (e.g., seal against) two other ring segments, or otherwise two ends of a single ring segment (e.g., if the ring includes only a total of two ring segments). For example, enlargements 601 and 601C may representone set of interfacing ring segments (e.g., sealing ring assembly 600 includes twelve interfaces, as illustrated), as worn over time. Referencing FIG. 6B, surface 613 may include a first surface area configured to seal against the bore as a contact surface (e.g., an initial value, when ring segment 460 is at a low to no wear condition). As sealing ring assembly 600 wears, ring segments 610 and 670 of FIG. 6B may wear to result in the configuration illustrated in FIG. 6C, wherein ring segments 610 and 670 are radially less thick in FIG. 6C than FIG. 6B (e.g., feature 611 has decreased in depth along radial dimension 602).

[0065] Feature 611 of ring segment 610 is labeled, and it will be understood that ring segment 610 may include another feature (not shown) that interfaces with ring segment 675. Additionally, ring segments 620, 630, 640, 650, and 660 may also include similar respective features as feature 611. Feature 611 includes a recess (e.g., a tapered slot), extending into surface 613. Feature 611 has a cross-section area formed by distances 690 and 691 that corresponds to a recess of surface 613. During wear, feature 611, illustrated as a blind recess, becomes shallower and corresponds to an increasing decrement of surface 613 (e.g., crosssection of distances 690 and 691 increases). To illustrate, during wear, the pocket formed by feature 611 may be increasingly exposed to, and filled with, pressurized gas from high- pressure region 150. The increase in radially outward area of feature 611, corresponding to the length and width (e.g., distance 691 and distance 690) allows the gas pressure in feature 611 to apply an increased pressure-based force radially inward on ring segment 610 (e.g., and collectively on sealing ring assembly 600).

[0066] In some embodiments, for example, a wear stabilization feature such as feature 611 includes a recess (e.g., a slot) arranged on a sealing segment (e.g., ring segment 610) in contact with the cylinder bore that opens a pocket as the ring wears. The recess (e.g., a slot, hole, or otherwise pocket) can be shaped such that it represents increased cross-sectional area in the azimuthal and axial directions 603 and 604 with wear. FIGS. 6A-6C, and similarly FIGS. 5A-5D, show an example of such illustrative features having such a recess geometry.

[0067] In an illustrative example, a sealing ring may include a sealing ring segment having at least one recess feature such as feature 611 extending from at least one sealing surface (e.g., surfaces 613) of a sealing ring segment, in which the feature is exposed to a high- pressure during operation. To illustrate, the at least one recess feature includes at least one slot. In some embodiments, the at least one recess feature includes a taper such that a blind end of the recess feature is wider than an open end of the recess feature (e.g., along radial direction 602).

[0068] In another illustrative example, a sealing ring may include a sealing ring segment having at least one slot embedded in an axially rearward surface of the sealing ring segment. The radially outward surface is arranged to contact a bore of a cylinder, for example. In some embodiments, the at least one slot includes one or more of a tapered or curved profile such that as material of the radially outward surface wears, the opening of the pocket increases.

[0069] FIGS. 7A-7B show several views of illustrative sealing ring assembly 700 and segments thereof, having a gas pocket, in accordance with some embodiments of the present disclosure. FIG. 7A shows a top view (e.g., radially inward), while FIG. 7B shows a front view (e.g., along an axial direction). Illustrated are axial direction 702, radial direction 704, and azimuthal direction 703. As illustrated, sealing ring assembly includes ring segments 710 and 720, which interface to each other and seal against a bore. It will be understood that sealing ring assembly 700 may include any suitable number ring segments. For example, sealing ring assembly may include 2N ring segments into total, with N segments similar to ring segment 710 and another N segments similar to ring segment 720 (e.g., arranged in an alternating manner), wherein N may be any suitable positing integer (e.g., one or greater than one). Accordingly, for 2N ring segments, the sealing ring assembly may include 2N interfaces between adjacent segments (e.g., in FIG. 8 A, N is illustratively equal to 4).

[0070] In an illustrative example, instead of filling the inter-segment gas pocket from the side, the high-pressure gas, from high-pressure region 150, can be fed (e.g., not shown in FIGS. 7A-7B, but shown in FIG. 8A-8C) through ring segment 710 on the high-pressure side to a closed hangar double slanted gas pocket formed by feature 711 that can be utilized to achieve wear stability action. Feature 711 includes an axial thickness of distance 790, an opening length of distance 791, a blind-end length of distance 794, and a depth of distance 792. To illustrate, feature 711 may be open to the high-pressure side by an area defined by distances 790 and 791 (e.g., an open area). Feature 711 may include a double-slanted, hangar geometry to help increase a size of the gas-pressurized region at the contact surface (e.g., a cylinder wall) with wear. For example, the area defined by distances 790 and 791 (e.g., the surface area of the portion of the inter-segment pocket that can accommodate pressurized gas) increases with ring wear. The increasing surface area of high-pressure gas on ring segment 710 reduces the overall outwards force on ring segment 710, thus reducing contact pressure along the sealing surface (e.g., surface 713 of ring segment 710). To illustrate, surfaces 713 of ring segment 710 and surface 723 of ring segment 723 are configured to seal against bore 162. During operation, gas from high-pressure region 150 may enter the openarea (e.g., defined by distances 790 and 791) and fill the volume of feature 711, applying a pressure force along the blind surface having length 794 (e.g., the effective or characteristic length of high-pressure acting on the blind surface may be equivalent to distance 791), which increases with wear. For example, the force applied from the gas may be equivalent to the gas pressure multiplied by the area of distance 791 by 790 projected onto the blind surface (e.g., having a geometric length of distance of 794).

[0071] FIGS. 8A-8C show several views of illustrative sealing ring assembly 800 and segments thereof, having a gas pocket of hangar geometry in an inter-segment region, in accordance with some embodiments of the present disclosure. For example, sealing ring assembly 700 of FIGS. 7A-7C may be similar to, the same as, or otherwise part of sealing ring assembly 800. Axial direction 803, radial direction 802, and azimuthal direction 804 are illustrated in FIG. 8A. As illustrated in FIG. 8A, sealing ring assembly 800 includes ring segments 810, 820, 830, 840, 850, 860, 870, and 880. For example, ring segments 810, 820, 830, and 840 are of a first type (e.g., similar to each other), and ring segments 850, 860, 870, and 880 are of a second type (e.g., similar to each other). While sealing ring assembly 800 is illustrated as having eight segments in total, with four segments of each type, a sealing ring assembly may include any suitable number and types of segments in accordance with the present disclosure. For example, a sealing ring assembly may include one ring segment of each type, or N segments of each type where N is a suitable positive integer greater than one.

[0072] FIGS. 8B-8C show perspective views of ring segment 810 and ring segment 850 at two successive states of wear, indicated by ring segment 810 (e.g., least worn), ring segment 810C (e.g., most worn). It will be understood that some hidden lines in FIGS. 8B-8C are omitted for purposes of clarity. As illustrated, ring segment 810 includes feature 811 arranged in surface 813, which is configured to seal against bore 162. For example, surface 813 of ring segment 810 and surface 863 of ring segment 860, along with corresponding surfaces of the other ring segments, are configured to seal against bore 162. Feature 811 of ring segment 810 is labeled, and it will be understood that ring segment 810 may include another similar feature interfacing to ring segment 850. In a further example, ring segments 820, 830, and 840 may also include similar respective features as feature 811. As sealing ring assembly 800 wears, ring segment 810 may wear to result in ring segment 810C, wherein segment 810C is radially less thick than ring segment 810, and feature 811 is opened such that distance 891 increases (e.g., feature 811 may open azimuthally).

[0073] Also illustrated in FIGS. 8B-8C, ring segment 810 includes channel 812 connection the volume of feature 811 to surface 816 (e.g., an axially forward surface) of ring segment810. For example, channel 812 may be open to a high-pressure region (e.g., high-pressure region 150). To illustrate, the length of distances 891 (which changes) and the opening size of channel 812 may govern the gas pressure in the volume of feature 811 (e.g., based on filling and venting dynamics). Accordingly, channel 812 may be sized to improve wear stability.

[0074] In an illustrative example, a ring segment (e.g., ring segment 810) may include a pocket (e.g., feature 811) arranged on a surface (e.g., surface 813) of the sealing ring segment arranged to contact a second surface of a different sealing ring segment (e.g., ring segment 860). To illustrate, the pocket may be in fluid communication with a pressurized region (e.g., open to the front of the ring), and the pocket may include a hangar geometry (e.g., a trapezoidal geometry) that increases gas pressurization area as the surface wears. In some embodiments, one or more slanted pressure saturation gas pockets (e.g., feature 811) embedded in a sealing surface (e.g., surface 813) of the sealing ring segment (e.g., ring segment 810) include one or more respective openings (e.g., along distance 891) that each increase in respective length as the sealing surface wears.

[0075] FIGS. 9A-9B show two perspective views of a portion of illustrative ring segment910 having a tapered groove (e.g., feature 911), at two stages of wear, in accordance with some embodiments of the present disclosure. For example, FIG. 9B illustrates ring segment 910B after some wear relative to ring segment 910, wherein radial thickness 990 is relatively reduced and feature 911 is relatively opened (e.g., because length 992 is greater than length 991). To illustrate, any of the illustrative ring segments of the present disclosure may include a feature such as feature 911. As illustrated, feature 911 includes an azimuthal length 991 at an open end, an azimuthal length 992 at a blind end, an axial thickness 993, and a radial depth 994. Channels 912 extend from surface 914 to a volume of feature 911, and feature911 is arranged at surface 913 configured to seal against bore 162. Region 919 corresponds to a region over which the gas pressure acts, applying a radially inward force on ring segment 910. For example, region 919 may be the same as or larger than a radially outer cross- sectional area of feature 911 (e.g., at bore 162).

[0076] In an illustrative example, feature 911 corresponds to a recess feature. The recess may include a first portion configured to open to bore 162 (e.g., feature 911), and a second portion that extends to a high-pressure region (e.g., channel 912). In some embodiments, feature 911 is a pressure-compensation groove that may be used for graphite seals to fill an area of surface 913 with high pressure gas (e.g., from high-pressure region 150) in order to reduce the wear rate. The ends of the grooves may be machined in a trapezoidal or slantedshape as shown in FIGS. 9A-9B to achieve a wear stability action similar to that illustrated in FIGS. 4A-4D. As the contact surface (e.g., surface 913) wears down, region 919 filled with gas pressure increases and reduces the contact pressure on surface 913.

[0077] FIG. 9C shows a cross-section view of illustrative sealing ring assembly 900 that includes ring segments 910 and 920. Coordinate axes 970 (i.e., radial), and 972 (i.e., axial) are provided in FIG. 11 for purposes of clarity. Sealing ring assembly 900 includes front ring 920 and rear ring 910. Sealing ring assembly 900 is configured to be arranged in a ring groove of piston 110, for example. In some embodiments, feature 911 is configured to balance radial forces. As illustrated, feature 911 is tapered. In some embodiments, feature 911 may be tapered in the axial direction, azimuthal direction, or both. Illustrative radial pressure fields 960 (i.e., acting radially inward) and 962 (i.e., acting radially outward) may act on sealing ring assembly 900 during operation. Radial pressure field 962 is directed radially outward and is created by gas from high-pressure region 150 acting on the radially inner surface of sealing ring assembly 900. Radial pressure field 960 is directed radially inward and is created by gas in the clearance between sealing ring assembly 900 and bore 162. Radial pressure field 960 is relatively larger than it would otherwise be without feature 911, which allows high-pressure gas to flow and affect radial pressure field 960. The resultant force 940 is directed radially outward, pushing sealing ring assembly 900 radially outward. The magnitude of resultant force 940 is lesser than it would otherwise be without feature 911. Resultant force 940 affects contact pressure between a region of contact of ring segment 910 (e.g., surface 913) and bore 162. In some embodiments, the farther towards the rear (axially) of sealing ring assembly 900 that feature 911 is located, the more resultant force 940, and hence wear, may be reduced. In some embodiments, feature 911 may be located in the rear half of sealing ring assembly 900, axially. It will be understood that the pocket location may be located at any suitable axial position (e.g., centered about any suitable axial position). In some embodiments, to help reduce wear, feature 911 may extend over as much of the circumferential extent of sealing ring assembly 900 as possible. In some embodiments, feature 911 need not intersect splits in sealing ring assembly 900 or otherwise in ring segment 910 (e.g., which may cause increased gas leakage and a poorer seal). For example, in some embodiments, feature 911 may extend most, but not all, of the way around sealing ring assembly 900 or otherwise along ring segment 910. In some embodiments, feature 911 may be pressurized at, or near to, the pressure of high-pressure region 150. In some embodiments, a hole or other passage (e.g., channels 912) may be formed (e.g., drilled) axially throughsealing ring assembly 900, thus connecting feature 911 to an axially front surface (e.g., surface 914) of the sealing ring assembly 900.

[0078] FIGS. 10A-10B show two perspective views of a portion of illustrative ring segment 1010 having one or more blind recesses (e.g., or more features 1012), at two stages of wear, in accordance with some embodiments of the present disclosure. For example, FIG. 10B illustrates ring segment 1010B after some wear relative to ring segment 1010, wherein radial thickness 1094 is relatively reduced and feature 1012 is opened to surface 1013, which is configured to seal against bore 162. To illustrate, any of the illustrative ring segments of the present disclosure may include a feature such as one or more features 1012. As illustrated, each of one or more features 1012 includes a blind hole extending axially from surface 1014 at the front of the ring and configured to be exposed to high-pressure region 150. As ring segment 1010 wears to result in ring segment 1010B, one or more features 1012 are exposed to surface 1013, forming respective openings 1017. Feature 1011 may be the same as feature 911 of FIGS. 9A-9B.

[0079] In an illustrative example, wear stability may be achieved using holes (e.g., one or more features 1012) formed (e.g., machined, molded, cast, or otherwise suitably formed) on the sealing ring (e.g., into surface 1014) that are configured to exchange mass with the incylinder gas (e.g., of high-pressure region 150). One or more features 1012 may be referred to as wear stabilizing holes (WSHs). In the beginning of ring wear life, a WSH need not have an impact on the sealing surface contact pressure. For example, as illustrated in FIG. 10 A, one or more features 1012 need not be open to surface 1013 initially. After some wear, as shown in FIG. 10B, one or more features 1012 may form openings 1017 in surface 1013. As the contact surface (e.g., surface 1013) wears, a WSH is exposed to the contact surface, as illustrated in FIG. 10B. Given that the gas pressure in the WSH is the same as or near to the in-cylinder pressure (e.g., of high-pressure region 150), this exposure may lower the sealing surface contact pressure (e.g., between surface 1013 and bore 162). A WSH’s radial and azimuthal position in surface 1014, as well as its axial length, may be tuned to improve the wear stability across a segmented ring pack.

[0080] In an illustrative example, a ring segment (e.g., ring segment 1010) may include one or more blind holes (e.g., one or more features 1012) arranged on a surface (e.g., surface 1014), where another surface (e.g., surface 1013) is configured to contact bore 162. The openings of the one or more blind holes become exposed to bore 162 with wear of the radially outer sealing surface (e.g., as surface 1013 wears, features 1012 become exposed to bore 162).

[0081] The proposed features in this disclosure achieve wear stability by increasing contact area (Mode I), increasing surface area exposed to gas pressurization on the contact surface (Mode II) with wear, or both. Functionally, both of these modes reduce the contact pressure on the sealing surface. Some non-limiting structural and functional physical features through which this is achieved are listed below:1. A protruding feature arranged on the low-pressure side of the seal that increases contact area with wear (e.g., the feature may have axial and radial taper to achieve this effect).2. A slot cut on the high-pressure side of the seal that increases contact area with wear.3. A side-fed inter-ring gas pocket with increasing opening length on the outer surface with wear that increases gas pressurization area on the outer surface with wear.4. A closed-fed inter-ring gas pocket with hangar geometry that increases gas pressurization area on the outer surface with wear.5. A slanted pressure saturation gas pocket that increases in length with wear.6. A blind hole arranged on an axial surface of a segment that become exposed (to the outer surface) with wear.

[0082] Illustrative benefits over current sealing ring assemblies as provided by the aforementioned sealing ring features may include one or more of the following:1. Segmented designs equipped with wear stability may experience lower strain than full-hoop solid lubricant seals, which may translate to a longer life and lower risk of breakage.2. Wear stability features increase the life of the seal by avoiding runaway problems, by tending to equalize the wear between sealing ring segments.3. Minimal changes may be needed in an existing segmented design to achieve wear stabilization because the wear stability features don’t require any additional component (e.g., may require some additional machining, molding, casting, or otherwise different or alternate processing of an existing component).

[0083] It will be understood that a ring segment may include one or more of the features of the present disclosure, and that various ring segments of a sealing ring assembly may include different features, the same features, or some of the same features. For example, a ring segment such as ring segment 310 or 610 may include a feature such as feature 611 (e.g., arranged to overlap an end of an adjacent ring segment) and also a feature such as feature 316 (e.g., arranged between ends of two adjacent ring segments, one on either side). In a further example, a ring segment such as ring segment 310 or 710 may include a feature such asfeature 711 (e.g., arranged to overlap an end of an adjacent ring segment) and also a feature such as feature 316 (e.g., arranged between ends of two adjacent ring segments, one on either side). In a further example, a ring segment such as ring segment 360, 460, 670, or 860 may include a feature such as feature 461 (e.g., arranged along a sealing surface), feature 911 (e.g., arranged in a sealing surface), channel 912 (e.g., arranged at a surface exposed to a high-pressure region), feature 1011 (e.g., arranged in a sealing surface), or feature 1012 (e.g., arranged to open to a sealing surface as the ring segment wears). In a further example, a sealing ring assembly may include (i) a first ring segment such as ring segment 310, 410, 510, 610, 710, or 810 that includes one or more of features 316, 511, 611, 711, or 811, and (ii) an interfacing or second ring segment such as ring segment 360, 460, 520, 670, 720, 860, 910, or 1010 that includes one or more of features 461, 911, 1011, or 1012, and optionally channels 912.

[0084] It will be understood that the present disclosure is not limited to the embodiments described herein and can be implemented in the context of any suitable system. In some suitable embodiments, the present disclosure is applicable to reciprocating engines and compressors. In some embodiments, the present disclosure is applicable to free-piston linear generators, engines, and compressors. In some embodiments, the present disclosure is applicable to combustion and reaction devices such as a reciprocating engine, free-piston engine, and linear generator. In some embodiments, the present disclosure is applicable to non-combustion and non-reaction devices such as reciprocating compressors and free-piston compressors. In some embodiments, the present disclosure is applicable to linear reciprocating devices with driver sections (e.g., gas springs). In some embodiments, the present disclosure is applicable to oil-free reciprocating and free-piston engines and compressors. In some embodiments, the present disclosure is applicable to oil-free free- piston engines with internal or external combustion or reactions. In some embodiments, the present disclosure is applicable to oil-free free-piston engines that operate with compression ignition (e.g., homogeneous charge compression ignition (HCCI), stratified charge compression ignition (SCCI), or other compression ignition), spark ignition, or both. In some embodiments, the present disclosure is applicable to oil-free free-piston engines that operate with gaseous fuels, liquid fuels, or both. In some embodiments, the present disclosure is applicable to linear free-piston engines. In some embodiments, the present disclosure is applicable to engines that can be combustion engines with internal combustion / reaction or any type of heat engine with external heat addition (e.g., from a heat source or external reaction such as combustion).

[0085] The foregoing is merely illustrative of the principles of this disclosure, and various modifications may be made by those skilled in the art without departing from the scope of this disclosure. The above-described embodiments are presented for purposes of illustration and not of limitation. The present disclosure also can take many forms other than those explicitly described herein. Accordingly, it is emphasized that this disclosure is not limited to the explicitly disclosed methods, systems, and apparatuses, but is intended to include variations to and modifications thereof, which are within the spirit of the following claims.

Claims

What is Claimed is:

1. A ring segment comprising: a first surface configured to seal against a bore of a cylinder; a second surface facing radially outward and arranged radially inward of the first surface; and at least one feature extending radially outward from a base coplanar with the second surface to the first surface.

2. The ring segment of claim 1, wherein the at least one feature comprises a pedestal.

3. The ring segment of claim 1, wherein the at least one feature comprises at least one of an axial taper or a radial taper.

4. The ring segment of claim 1, the at least one feature comprises at least three surfaces.

5. The ring segment of claim 1, wherein: the second surface extends azimuthally towards opposite ends of the ring segment; the second surface is configured to interface to at least one other sealing ring segment; and the second surface is configured to be exposed to a low-pressure region of the bore.

6. The ring segment of claim 1, wherein: the at least one feature comprises a radially outward surface; and the radially outward surface comprises a surface area lesser than an area of the base.

7. The ring segment of claim 1, further comprising a radial thickness extending from a radially inward surface to the first surface, wherein: the at least one feature comprises a radially outward surface comprising an area; the radial thickness is configured to decrease as the ring segment wears against the bore; and the area is configured to increase as the as the ring segment wears against the bore.

8. The ring segment of claim 1, wherein:the first surface comprises a first area; the at least one feature comprises a radially outward surface comprising a second area; and the at least one feature is configured to increase a summation of the first area and the second area as the ring segment wears against the bore.

9. The ring segment of claim 1, further comprising a third surface extending radially outward from the second surface to the first surface, wherein the third surface is axially rearward facing, and wherein the third surface is configured to seal against a second ring segment.

10. A sealing ring assembly comprising a first ring segment comprising: a first surface configured to seal against a bore of a cylinder; a second surface facing radially outward and arranged radially inward of the first surface; and at least one feature extending radially outward from a base coplanar with the second surface to the first surface; and a second ring segment configured to seal against the second surface and against the bore.

11. The sealing ring assembly of claim 10, wherein the at least one feature comprises at least one of an axial taper or a radial taper.

12. The sealing ring assembly of claim 10, wherein: the second surface extends azimuthally towards opposite ends of the first ring segment; and the second surface is configured to be exposed to a low-pressure region of the bore.

13. The sealing ring assembly of claim 10, wherein: the at least one feature comprises a radially outward surface; and the radially outward surface comprises a surface area lesser than an area of the base.

14. The sealing ring assembly of claim 10, wherein:the first ring segment further comprises a radial thickness extending from a radially inward surface to the first surface; the at least one feature comprises a radially outward surface comprising an area; the radial thickness is configured to decrease as the first ring segment wears against the bore; and the area is configured to increase as the as the first ring segment wears against the bore.

15. The sealing ring assembly of claim 10, wherein: the first surface comprises a first area; the at least one feature comprises a radially outward surface comprising a second area; and the at least one feature is configured to increase a summation of the first area and the second area as the first ring segment wears against the bore.

16. The sealing ring assembly of claim 10, wherein: the first ring segment further comprises a third surface extending radially outward from the second surface to the first surface; the third surface is axially rearward facing; and the third surface is configured to seal against the second ring segment.

17. A device comprising: a cylinder comprising a bore; a piston configured to move along the bore and comprising a ring groove; and a sealing ring assembly arranged in the ring groove, wherein the sealing ring assembly comprises a ring segment comprising: a first surface configured to seal against the bore; a second surface facing radially outward and arranged radially inward of the first surface; and at least one feature extending radially outward from a base coplanar with the second surface to the first surface.

18. The device of claim 17, wherein:the ring segment further comprises a radial thickness extending from a radially inward surface to the first surface; the at least one feature comprises a radially outward surface comprising an area; the radial thickness is configured to decrease as the ring segment wears against the bore; and the area is configured to increase as the as the ring segment wears against the bore.

19. A ring segment comprising: a sealing surface configured to seal against a bore of a cylinder; and at least one feature comprising: a first surface configured to seal against the bore and increase in contact area during wear; and a second surface configured to be exposed to a low-pressure region of the bore and decrease in area during wear.

20. The ring segment of claim 19, further comprising an inner surface facing radially outward and arranged radially inward of the sealing surface, wherein the at least one feature extends radially outward from a base coplanar with the inner surface to the sealing surface.

21. A ring segment comprising: a first surface configured to seal against a bore of a cylinder, wherein the first surface comprises a first area; and a recess arranged at the first surface, wherein: the recess defines a second area; and the second area is configured to increase during wear of the ring segment.

22. The ring segment of claim 21, wherein: the recess is configured to be exposed to a high-pressure gas of the bore; and the recess is configured to cause a contact pressure between the bore and the first surface to be decreased based on the high-pressure gas.

23. The ring segment of claim 21, further comprising a second surface arranged radially inward of the first surface, wherein the second surface is configured to be exposed to a high- pressure gas of the bore.

24. The ring segment of claim 21, wherein the recess is fluidly coupled to a third surface of the ring segment configured to contact a high-pressure region of the bore.

25. The ring segment of claim 24, further comprising a blind recess arranged along the third surface, wherein the blind recess forms an opening in the first surface to become exposed to the bore during wear.

26. The ring segment of claim 25, wherein, before wear, the blind recess is closed to the bore and is closed to the first surface.

27. The ring segment of claim 21, wherein: the recess comprises a first portion having a cross-sectional area that decreases in a radially outward direction; the second area corresponds to a radially outermost cross-sectional area of the cross- sectional area; and the recess comprises a second portion extending from a front surface of the ring segment to an axial face of the first portion of the recess.

28. A ring segment comprising: a first surface comprising a contact area configured to seal against a bore of a cylinder; and a recess arranged in the first surface, wherein: the recess is open to a low-pressure region of the bore; the recess comprises a radially outer cross-sectional area configured to decrease during wear; and the recess is configured to cause the contact area to increase during wear.

29. The ring segment of claim 28, wherein the recess comprises a slot open to the bore and to an axially rearward surface of the ring segment.

30. A ring segment comprising: a first surface comprising a contact area configured to seal against a bore of a cylinder;a second surface configured to seal against another ring segment; and a recess arranged in the second surface, wherein: the recess is open to a high-pressure region of the bore; and the recess comprises a radially outer cross-sectional area configured to increase during wear.

31. The ring segment of claim 30, wherein the recess comprises a pocket having at least one slanted face.

32. The ring segment of claim 30, wherein: the recess comprises a cross-sectional area that decreases in a radially outward direction; and the radially outer cross-sectional area corresponds to a radially outermost cross- sectional area of the cross-sectional area.

33. The ring segment of claim 30, wherein the recess is open to the bore and open to an azimuthal surface of the ring segment.

34. The ring segment of claim 30, wherein: the recess is initially arranged radially inward from the first surface such that the recess initially avoids contact with the bore; and after at least some radial wear, the recess opens to the first surface to contact the bore.

35. A sealing ring assembly comprising: any of the ring segments of claims 19-34 as a first ring segment; and a second ring segment configured to interface to the first ring segment.

36. A device comprising: a sealing ring assembly comprising: any of the ring segments of claims 19-34 as a first ring segment; and a second ring segment configured to interface to the first ring segment. the cylinder comprising the bore; and a piston configured to move along the bore and comprising a ring groove, wherein the sealing ring assembly is arranged in the ring groove.

37. The ring segment of any of claims 19-34, wherein the ring segment is configured for oil-less operation.

38. The ring segment of any of claims 19-34, wherein the ring segment comprises a selflubricating material.

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