Patent Description:
Seals for piston-cylinder devices separate high-pressure gas in the cylinder at one end of the piston from lower pressure gas at the other end of the piston. Typically, this seal consists of a ring, or rings, that sit in circumferential grooves in the outer piston surface. As the piston and seal reciprocate in the cylinder, the outer surface of the seal element may come in sliding contact with the inner surface of the cylinder. Friction between the seal and the cylinder wall occurs at this sliding interface and can result in wear-related failures such as, for example galling, scuffing, or seizing between the seal and cylinder. A widespread solution to this problem is to apply a film of lubricating fluid such as oil to the interface between the seal and the cylinder.

The use of a self-lubricating material for the seal can reduce scuffing or galling failures but introduces at least two significant problems. First, self-lubricating materials generally have low inherent material strength and are prone to failures by breakage when subjected to a high-pressure differential. Second, the seal material generally wears down quickly, resulting in gaps opening thus allowing leakage of the gas being sealed. The wear may further result in large amounts of crevice volume in the piston groove as the seal moves radially outward to maintain a seal as seal material is removed. The relatively high rate of wear is inherent and fundamental to use of the self-lubricating material because material must be removed from the seal element to access the lubricating properties.

US Patent application number: <CIT> Al discusses "The piston ring (<NUM>) for a dry-running piston compressor consists of a first and a second ring part (<NUM> a, <NUM> b) having gaps or butt joints (<NUM> e, <NUM> f). These two ring parts (<NUM> a, <NUM> b) are arranged to lie mutually concentric with respect to an axis (C). The first ring part (<NUM> a) has an essentially L-shaped cross-section, having a first arm (<NUM>) running in the direction of the axis (C) and a second arm (<NUM>) extending outwards in a direction essentially radial to the axis (C)", and discloses a sealing ringset according to the preamble of claim <NUM>.

The present disclosure is directed to a sealing ringset as set out in the appended claims. The sealing ringset may be configured to seal against a bore of a cylinder without oil. The sealing ringset includes at least one sealing ring and at least one applicator. The at least one sealing ring is configured to be arranged on a piston to seal against the bore, wherein the at least one sealing ring is a metal ring. The applicator includes a solid lubricant and is configured to be arranged on the piston. The applicator provides lubrication between the at least one sealing ring and the bore by wearing against the bore.

In some embodiments, the at least one sealing ring and the applicator are configured to be arranged together in a circumferential groove of the piston.

In some embodiments, the at least one sealing ring and the applicator are configured to be arranged in respective circumferential grooves of the piston.

In some embodiments, the at least one sealing ring is axially rearward of the applicator.

In some embodiments, the at least one sealing ring is axially forward of the applicator.

In some embodiments, the applicator is not configured to act as a seal.

In some embodiments, the applicator comprises an oxidation inhibitor.

In some embodiments, the applicator is configured to provide lubrication between the at least one sealing ring and the bore by depositing a layer of the solid lubricant on the bore.

In some embodiments, the sealing ringset includes a spring arranged radially inwards of the applicator and configured to apply a radially outward force on the applicator.

In some embodiments, the at least one sealing ring comprises a first sealing ring, and the sealing ringset includes a second sealing ring. The second sealing ring includes a solid lubricant and is configured to prevent the first sealing ring from contacting a ring groove.

In some embodiments, the present disclosure is directed to a piston assembly. The piston assembly includes a piston having at least one circumferential groove and a sealing ringset. The sealing ringset includes at least one sealing ring and an applicator. In some embodiments, the at least one sealing ring is configured to be arranged in the at least one circumferential groove, wherein the at least one sealing ring is a metal ring. The at least one sealing ring is configured to seal against a bore without oil. The applicator includes a solid lubricant and is configured to be arranged in the at least one circumferential groove. The applicator is configured to provide lubrication between the at least one sealing ring and the bore by wearing against the bore. In some embodiments, the at least one circumferential groove consists of a single groove, and the at least one sealing ring and the applicator are configured to be arranged together in the single groove. In some embodiments, the at least one circumferential groove includes at least two grooves, and the at least one sealing ring and the applicator are configured to be arranged in respective circumferential grooves of the piston.

In some embodiments, the present disclosure is directed to a device including a cylinder, a piston, and a sealing ringset. The cylinder includes a bore. The piston includes at least one circumferential groove and is configured to move axially within the bore. The sealing ringset includes at least one sealing ring and an applicator. The at least one sealing ring is configured to be arranged in the at least one circumferential groove, wherein the at least one sealing ring is a metal ring. The at least one sealing ring is also configured to seal against the bore without oil. The applicator includes a solid lubricant and is configured to be arranged in the at least one circumferential groove. The applicator is configured to provide lubrication between the at least one sealing ring and the bore by wearing against the bore.

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. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale.

In some embodiments, the present disclosure is directed to a sealing ringset configured for sealing a gas in a high-pressure region of a piston and cylinder device, more particularly in the absence of a liquid lubricant material (e.g., oil). According to the invention, a metal is used as the seal element (e.g., a ring), with a separate solid-lubricant applicator arranged in a groove of the piston. By separating the sealing and lubricating functions, materials can be selected independently (e.g., and may be optimized for each particular function). For example, the sealing element is constructed of a high-strength material and thus can support pressure loads from high-pressure gas without breaking. The sealing element can also be made of a relatively hard, wear-resistant material on its sliding surface (e.g., its radially outer surface configured to seal against a bore), thus minimizing, or otherwise reducing, the radial wear experienced by the sealing element. A separate solid-lubricant applicator is located on the piston and is configured to reduce scuffing and other friction-related failures that would occur with such a material of the sealing element in the absence of lubrication. For example, as the piston reciprocates in the bore, the solid-lubricant applicator slides against the cylinder bore and applies solid lubricant material to the bore by wearing against the bore. A solid lubricant film results on the bore, against which the sealing element may slide. The solid-lubricant applicator need not function as the sealing element, or otherwise provide any sealing functionality, and therefore gaps and volumes that open as a result of wear of the applicator do not necessarily result in increased leakage. Further, because the applicator is not required to perform the sealing function, the applicator is not required to withstand the same pressure and thermal loads as the sealing element, and therefore, in some circumstances, the material strength limitations inherent to the solid lubricant material does not impact the sealing function greatly, if at all.

The term "seal" as used herein, refers to the creation, maintenance, or both of a high-pressure region and a low-pressure region. For example, a seal may include a sealing ring assembly that is configured to reduce a leakage rate of gas from a high-pressure region to a low-pressure region, by limiting flow between a high-pressure boundary and a low-pressure boundary of the seal. Accordingly, a seal can be defined in terms of its constraints on a leakage rate. It will be understood that a seal, such as a sealing ring assembly, as described herein, may have any suitable corresponding leakage rate. For example, in some circumstances, a relatively worse seal may allow more leakage, but may be acceptable based on one or more relevant performance criterion. In a further example, a sealing ring assembly configured for high efficiency operation of a piston and cylinder device may have a relatively low leakage rate (e.g., be a more effective seal).

As used herein, a "ring segment" shall refer to a sealing element extending for an azimuthal angle greater than zero degrees, having a radially outer surface, and configured to seal at least along a portion of the radially outer surface against a bore. A ring segment may include end faces, if not azimuthally contiguous around the full bore.

As used herein, a "ring" shall refer to a sealing element including at least one ring segment, which may be, but need not be, azimuthally contiguous along a bore. For example, a ring may include one ring segment, in which case these terms overlap. In a further example, a ring may include four ring segments, in which case the ring refers to the collective of the four ring segments. A ring may include, but need not include, one or more interfaces between one or more ring segments. A "ring" shall also refer to a sealing element including at least one ring segment configured to seal against a land of a piston.

As used herein, a "sealing ringset," also referred to as a "ringset," shall refer to a collection of one or more rings and one or more applicators, configured to engage with a piston, move along a bore, and seal between a high-pressure region and a low-pressure region of the bore. A sealing ringset may include more than one ring, each configured to act as a seal. A sealing ringset may include one or more solid lubricants applicator configured to aid the one or more rings in sealing. In some embodiments, an applicator need not act as a seal, but is configured to enable one or more rings to act as a seal (e.g., by providing lubricant to prevent seizing). In some embodiments, an applicator may provide at least some sealing functionality.

<FIG> shows a cross-sectional view of illustrative piston and cylinder assembly <NUM>, including a sealing ringset, in accordance with some embodiments of the present disclosure. Cylinder <NUM> includes bore <NUM>, which is the inner cylindrical surface in which piston assembly <NUM> travels (e.g., along axis <NUM>). Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM> and <NUM> (e.g., which may be annular), in which respective ring <NUM> and applicator <NUM> are configured to be arranged and translate with piston <NUM>. Grooves <NUM> and <NUM> may be similar in shape, but need not be. Ring <NUM> and applicator <NUM> constitute an illustrative ringset. As piston assembly <NUM> translates along axis <NUM> (e.g., during an engine cycle), in cylinder <NUM>, the gas pressure in high-pressure region <NUM> may change (e.g., high-pressure region <NUM> may be closed with a cylinder head or an opposing piston). For example, as piston assembly <NUM> moves to the left, as illustrated, the pressure in high pressure region <NUM> may increase. Low-pressure region <NUM>, located to the rear (e.g., axis <NUM> is directed in the rearward direction) of the sealing ring assembly may be at a gas pressure below the pressure of high pressure region <NUM> for at least some, if not most, of a stroke or cycle of the piston assembly <NUM> in cylinder <NUM>. The pressure ranges in high pressure region <NUM> and low-pressure region <NUM> may be any suitable ranges (e.g., sub-atmospheric pressure to well over <NUM> 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 <NUM> may interact flow-wise with intake or exhaust ducting that is in communication with ports <NUM> or <NUM>, and be maintained relatively near pressure in the ducting. In an illustrative example, low pressure region <NUM> 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 <NUM> 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 the ringset refers to the face or portion axially nearest high-pressure region <NUM>, and the "rear" of the ringset refers to the face or portion axially nearest low-pressure region <NUM>.

It will be understood that unless otherwise specified, all pressures referred to herein are in absolute units (e.g., not gage or relative).

In some embodiments, low-pressure region <NUM> may include, communicate gas pressure with, or otherwise be open to ports <NUM> and <NUM> for gas exchange. For example, ports <NUM> and <NUM> may be exhaust ports, intake ports, or both. Ports may be, but need not be, opened and closed using valves. For example, in some embodiments, ports <NUM> and <NUM> refer to openings coupled to a manifold or other flow plenum, without valves included (e.g., flow is control by covering and uncovering ports <NUM> and <NUM> by ring <NUM>). In a further example, in some embodiments, ports <NUM> and <NUM> refer to openings coupled to a manifold or other flow plenum, with valves included to control flow profiles and timing. The term "valve" may refer to any actuated flow controller or other actuated mechanism for selectively passing matter through an opening, including but not limited to: ball valves, plug valves, butterfly valves, choke valves, check valves, gate valves, leaf valves, piston valves, poppet valves, rotary valves, slide valves, solenoid valves, <NUM>-way valves, or <NUM>-way valves. Valves may be actuated by any means, including but not limited to: mechanical, electrical, magnetic, camshaft-driven, hydraulic, or pneumatic means.

Ring <NUM> maintains contact with bore <NUM>, or a layer of solid lubricant deposited thereon, to create the seal. Applicator <NUM> maintains contact with bore <NUM>, or a layer deposited thereon, to further deposit solid lubricant onto the surface. The rate at which sliding wear removes material from the radially outer surface of applicator <NUM> is also a function of the resulting contact pressure (e.g., higher contact pressure increases the wear rate). For example, an increase in the contact pressure corresponds to an increase in wear rate and deposition rate. Deposited material from applicator <NUM> lubricates the interface between bore <NUM> and ring <NUM>. Accordingly, piston and cylinder assembly <NUM> is configured to operate without liquid for lubrication (e.g., oil or synthetic oil). Components of a ringset that are referred to herein to be in contact with a bore may be in contact with a layer deposited on the bore, or both the layer and the bore. It will be understood that in the context of sealing, forces, and friction, the phrase "seal against a bore" also includes sealing against the layer deposited on the bore, or sealing against both the layer and the bore. To illustrate, the cylinder wall material (e.g., steel or other metal) need not actually be in contact with a ring or an applicator, but rather a surface layer of solid lubricant may be in contact with the ringset.

It will be understood that high-pressure and low-pressure may refer to transient pressure states of a piston and cylinder device. For example, referencing an engine cycle, the high-pressure boundary of a sealing ring assembly may have a pressure greater than a low-pressure boundary of the sealing ring assembly for most of the engine cycle (e.g., except 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. 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 ringset may seal differently at different positions in a cycle. For example, a ringset may always seal a high-pressure region from a low-pressure region. In a further example, a ringset 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 some embodiments, piston <NUM> may be an open-faced piston. For example, piston <NUM> may include (not shown) openings, cutouts, or other fluid paths from high pressure region <NUM> to groove <NUM>, groove <NUM>, or both. Accordingly, in some embodiments employing an open-faced piston, the inner radial surfaces (e.g., referencing radial direction <NUM> in <FIG>) of ring <NUM>, ring <NUM>, or both, may be exposed to gas pressure of high-pressure region <NUM>.

A ringset (e.g., ring <NUM> and applicator <NUM>) may include any suitable geometry and include any suitable number of rings, number of applicators, and number of ring grooves. For example, the ringset of <FIG> includes a single ring (i.e., ring <NUM>), a single applicator (i.e., applicator <NUM>), arranged in respective grooves (i.e., respective grooves <NUM> and <NUM>), in which ring <NUM> is arranged axially forward of applicator <NUM> on piston <NUM>. A ringset may include one or more rings, having a rectangular cross-section, or any other suitable non-rectangular cross section, or combination thereof. A ringset may include one or more rings each having any suitable arrangement of splits, interfaces, overlapping segments, or other features. For example, a ring may be segmented, and may include more than one ring segment, which are configured to mate to one another, or themselves, at respective interfaces to form the seal.

An applicator (e.g., applicator <NUM> of <FIG>) may be configured to apply any suitable solid lubricant material to a bore, in accordance with the present application. For example, an applicator may include graphite, impregnated graphite, an oxidation inhibitor, a polymer, hexagonal boron nitride, molybdenum disulfide, any other suitable material, or any combination thereof. For example, in the context of an internal combustion engine, the solid lubricant material may include graphite, including graphite materials that may be impregnated with a minority fraction of another material, such as an oxidation inhibitor (e.g., to prevent corrosion of a sealing ring, a bore of a cylinder, or both), a soft metal (e.g., Tin or Antimony), phenolics, or a polymer-resin. In a further example, in the context of lower-temperature applications such as compressors, the solid lubricant material may include a polymer, optionally with graphite embedded. In an illustrative example, applicator <NUM> may include graphite embedded in polytetrafluoroethylene (PTFE).

For example, as illustrated in <FIG>, applicator <NUM> consists of a circumferential ring made from the solid lubricant material. An applicator may include one or more splits to allow the applicator to expand radially as it wears, thus maintaining sliding contact with the bore. In some embodiments, a radial spring element (not shown in <FIG>) may be included and arranged radially inward of an applicator to apply a radially outward force on the applicator against the bore to ensure consistent and continued application of solid lubricant. As illustrated in <FIG>, ring <NUM> is arranged such that the gas pressure drop axially from high-pressure region <NUM> to low-pressure region <NUM> of the piston occurs primarily across ring <NUM> axially, rather than applicator <NUM>. Applicator <NUM> is arranged such that it does not need to function as a seal and does not need to experience the full pressure and temperature conditions of high-pressure region <NUM>. Although not shown in <FIG>, additional rings may be included on the piston downstream (i.e., rearward) of applicator <NUM>. For example, a second ring (not shown in <FIG>) may be included in a third groove (not shown in <FIG>), downstream of applicator <NUM> (e.g., as illustratively shown in <FIG>). Illustrated in <FIG> are some examples of ringsets including multiple rings.

Ring <NUM> may include a ductile material having a large tensile strength such as, for example, a metal. For example, ring <NUM> may include steel, stainless steel, a copper alloy, a high-temperature alloy (e.g., Inconel or other nickel alloys), a composite of several materials, a composite of several structures of material, any other suitable material or materials, or any combination thereof. In some embodiments, ring <NUM> may include a coating for wear resistance such as, for example, a thermal spray coating, a physical vapor deposition coating, a plating (e.g., chrome plating), a diamond-like carbon (DLC) coating, a surface treatment (e.g., nitriding or heat treating), any other suitable surface treatment for wear resistance, or any combination thereof. In some embodiments, ring <NUM> may include a split, allowing it to expand radially outward to match bore <NUM> and maintain a tight seal. Ring <NUM> is configured to slide on a film of solid lubricant deposited on bore <NUM> by applicator <NUM>.

<FIG> shows a cross-sectional view of illustrative piston and cylinder device <NUM>, including a sealing ringset arranged in multiple grooves, in accordance with some embodiments of the present disclosure. Cylinder <NUM> includes bore <NUM>, which is the inner cylindrical surface in which piston assembly <NUM> travels (e.g., along axis <NUM>). Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM> and <NUM>, in which respective ring <NUM> and applicator <NUM> are configured to be arranged and translate with piston <NUM>. Spring <NUM> (e.g., which may be ring-shaped) is arranged radially inward of applicator <NUM> and is configured to apply a radial force (i.e., a preload directed along or against axis <NUM>) on applicator <NUM> to affect a contact pressure between applicator <NUM> and bore <NUM> and layer <NUM> deposited thereon. Ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged downstream of applicator <NUM>, in respective groove <NUM>. Applicator <NUM> is configured to deposit solid lubricant to form, maintain, replenish, or add upon layer <NUM> (i.e., a solid lubricant layer). Applicator <NUM>, spring <NUM>, or both are configured to engage axially with land <NUM>, land <NUM>, or both of piston <NUM>. Ring <NUM> is configured to engage (e.g., contact) axially with land <NUM>, land <NUM>, or both of piston <NUM>. In an illustrative example, a spring (e.g., spring <NUM>) may include a cantilever beam spring (e.g., with one end fixed to piston <NUM> and the other configured to push applicator <NUM>), a coil spring, a disc spring, a wave spring, any other suitable spring, or any combination thereof.

<FIG> shows a cross-sectional view of illustrative piston assembly and cylinder <NUM>, including a sealing ringset arranged in a single groove, in accordance with some embodiments of the present disclosure. Cylinder <NUM> includes bore <NUM>, which is the inner cylindrical surface in which piston assembly <NUM> travels (e.g., along axis <NUM>). Piston assembly <NUM> includes piston <NUM>, which includes groove <NUM>, in which ring <NUM> and applicator <NUM> are configured to be arranged and translate with piston <NUM>. Spring <NUM> (e.g., also termed a radial spring) is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> to affect a contact pressure between applicator <NUM> and bore <NUM> and layer <NUM> deposited thereon. Ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged upstream of applicator <NUM> in groove <NUM>. Applicator <NUM> is configured to deposit solid lubricant to form, maintain, replenish, or add upon layer <NUM> (i.e., a solid lubricant layer). In some embodiments, ring <NUM> is configured to engage applicator <NUM> at their axial interface in groove <NUM>. Applicator <NUM>, spring <NUM>, or both are configured to engage axially with land <NUM>, land <NUM>, or both of piston <NUM> (e.g., by applying a contact force).

<FIG> shows a cross-sectional view of illustrative piston assembly <NUM>, including a sealing ringset arranged in three grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> is configured to travel along axis <NUM>. Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM>, <NUM>, and <NUM>, in which respective ring <NUM>, ring <NUM>, and applicator <NUM> are configured to be arranged respectively and translate with piston <NUM>. Spring <NUM> is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> (e.g., to affect a contact pressure between applicator <NUM> and a bore and/or layer of solid lubricant deposited thereon). Ring <NUM>, ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged downstream of applicator <NUM> and in groove <NUM>. Ring <NUM> is arranged downstream of ring <NUM> and in groove <NUM>. As shown <FIG>, while applicator <NUM> may experience a relatively smaller pressure drop during operation than that across either ring <NUM> or ring <NUM>, applicator <NUM> may still be subjected to the conditions of a high-pressure region (e.g., high temperatures and/or pressures).

<FIG> shows a cross-sectional view of illustrative piston assembly <NUM>, including a sealing ringset arranged in three grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> is configured to travel along axis <NUM>. Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM>, <NUM>, and <NUM>, in which respective ring <NUM>, ring <NUM>, and applicator <NUM> are configured to be arranged respectively and translate with piston <NUM>. Spring <NUM> is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> (e.g., to affect a contact pressure between applicator <NUM> and a bore and/or layer of solid lubricant deposited thereon). Ring <NUM>, ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged upstream of ring <NUM> and in groove <NUM>. Ring <NUM> is arranged upstream of applicator <NUM> and in groove <NUM>. As shown <FIG>, applicator <NUM> may experience a relatively smaller pressure drop during operation than that across either ring <NUM> or ring <NUM> and is not subjected to the full conditions of a high-pressure region (e.g., high temperatures and/or pressures) since it is downstream.

<FIG> shows a cross-sectional view of illustrative piston assembly <NUM>, including a sealing ringset arranged in two grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> is configured to travel along axis <NUM>. Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM> and <NUM>, in which ring <NUM>, ring <NUM>, and applicator <NUM> are configured to be arranged and translate with piston <NUM>. Spring <NUM> is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> (e.g., to affect a contact pressure between applicator <NUM> and a bore and/or layer of solid lubricant deposited thereon). Ring <NUM>, ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged upstream of applicator <NUM> and both are arranged in groove <NUM>. Ring <NUM> and applicator <NUM> are arranged upstream of ring <NUM>, which is arranged in groove <NUM>. As shown <FIG>, applicator <NUM> may experience a relatively smaller pressure drop during operation than that across ring <NUM> or ring <NUM> and may be subjected to partially reduced conditions of a high-pressure region (e.g., high temperatures and/or pressures) since it is between rings <NUM> and <NUM>. For example, applicator <NUM> may experience a pressure intermediate in value to that of the high-pressure region (i.e., to the left of piston <NUM> as illustrated) and a low-pressure region (i.e., to the right of piston <NUM> as illustrated).

<FIG> shows a cross-sectional view of illustrative piston assembly <NUM>, including a sealing ringset arranged in two grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> is configured to travel along axis <NUM>. Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM> and <NUM>, in which ring <NUM>, ring <NUM>, and applicator <NUM> are configured to be arranged and translate with piston <NUM>. Spring <NUM> is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> (e.g., to affect a contact pressure between applicator <NUM> and a bore and/or layer of solid lubricant deposited thereon). Ring <NUM>, ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged downstream of applicator <NUM> and both are arranged in groove <NUM>. Ring <NUM> and applicator <NUM> are arranged upstream of ring <NUM>, which is arranged in groove <NUM>. As shown <FIG>, applicator <NUM> may experience a relatively smaller pressure drop during operation than that across ring <NUM> or ring <NUM> and may be subjected to full conditions of a high-pressure region (e.g., high temperatures and/or pressures) since it is upstream of both rings <NUM> and <NUM>. For example, applicator <NUM> may experience (i.e., be exposed to at a surface) a peak pressure and temperature of the high-pressure region. In a further example, in some embodiments, spring <NUM> need not be included when applicator <NUM> is forward of both ring <NUM> and ring <NUM> (e.g., pressure from high-pressure region <NUM> may push the applicator radially outward).

<FIG> shows a cross-sectional view of an illustrative piston assembly, including a sealing ringset arranged in three grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> is configured to travel along axis <NUM>. Piston assembly <NUM> includes piston <NUM>, which includes grooves <NUM>, <NUM>, and <NUM>, in which respective ring <NUM>, ring <NUM>, and applicator <NUM> are configured to be arranged respectively and translate with piston <NUM>. Spring <NUM> is arranged radially inward of applicator <NUM> and is configured to apply a radial outward force (i.e., along axis <NUM>) on applicator <NUM> (e.g., to affect a contact pressure between applicator <NUM> and a bore and/or layer of solid lubricant deposited thereon). Ring <NUM>, ring <NUM>, applicator <NUM>, and spring <NUM> constitute an illustrative ringset. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>. Ring <NUM> is arranged upstream of applicator <NUM> and in groove <NUM>. Ring <NUM> is arranged downstream of applicator <NUM> and in groove <NUM>. Applicator <NUM> and spring <NUM> are arranged in groove <NUM> between ring <NUM> and ring <NUM>. As shown <FIG>, applicator <NUM> may experience a relatively smaller pressure drop during operation than that across ring <NUM> or ring <NUM> and is subjected to partially reduced conditions of a high-pressure region (e.g., high temperatures and/or pressures) since it is between rings <NUM> and <NUM>. For example, applicator <NUM> may experience a pressure intermediate in value to that of the high-pressure region and a low-pressure region.

<FIG> shows a perspective view of a portion of illustrative piston assembly <NUM>, including a sealing ringset arranged in three grooves, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> includes piston <NUM>, which includes three grooves into which respective ring <NUM>, applicator <NUM>, and ring <NUM> are configured to be arranged and translate with piston <NUM>. Ring <NUM> (e.g., which includes ring split <NUM>), ring <NUM>, and applicator <NUM> constitute an illustrative ringset. Ring <NUM> is arranged upstream of applicator <NUM>. Ring <NUM> is arranged downstream of applicator <NUM>. Applicator <NUM> is arranged in a groove between ring <NUM> and ring <NUM>. Gap <NUM> in applicator <NUM> may occur, widen, or otherwise persist during wear of applicator <NUM>. Because applicator <NUM> does not function as a seal, gap <NUM> need not significantly impact the seal formed by ring <NUM> and <NUM>. In some embodiments, the gas proximate to applicator <NUM> during operation is at a higher pressure than a low-pressure region (e.g., rearward of the piston), and there may be a relatively small pressure differential across applicator <NUM> (e.g., and relatively less loading) as compared to rings <NUM> and <NUM>. In some embodiments, gap <NUM> is angled such that no streak forms in the bore where solid lubricant is void. In some embodiments, a second applicator (e.g., or more applicators) may be included, with gaps misaligned to gap <NUM> (e.g. so that no gaps azimuthally align), to assist in more complete coverage of the solid lubricant on the bore. For example, a second applicator may be included on a piston, with its gap <NUM> degrees azimuthally from gap <NUM>, such that the gaps are misaligned.

<FIG> shows a perspective view of a portion of illustrative open-face piston assembly <NUM>, including a sealing ringset, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> includes open-face piston <NUM> and a sealing ringset. Ring <NUM> and applicator <NUM> constitute the ringset of <FIG>. Open-face piston <NUM> includes opening <NUM>, which opens to a radially inner face of the ringset and fluid couples the radially inner face to a high-pressure region.

<FIG> shows a cross-sectional view of illustrative open-face piston assembly <NUM>, including a sealing ringset arranged in a single groove, in accordance with some embodiments of the present disclosure. Piston assembly <NUM> may be similar to piston assembly <NUM> of <FIG>, for example. Piston assembly <NUM> includes open-face piston <NUM> and a sealing ringset. Ring <NUM>, ring <NUM>, and applicator <NUM> constitute the ringset of <FIG>. The sealing ringset defines high-pressure region <NUM> and low-pressure region <NUM>.

Applicator <NUM> is arranged in groove <NUM> such that it is free to move independently from the ring <NUM>, and thus can wear at a different rate from the metal seal. In some embodiments, gas pressure on the inner surface of applicator <NUM> (e.g., in region <NUM> which is open to high-pressure region <NUM>), during operation, pushes applicator <NUM> radially outward against a bore (e.g., similar to a spring ring), causing solid lubricating material to be transferred from applicator <NUM> to the bore. Ring <NUM> is thus lubricated against the bore by the deposited film from applicator <NUM>. In some embodiments, region <NUM> need not be appreciably open to high-pressure region <NUM> for a radially outward pressure force to push applicator <NUM> radially outwards. In some embodiments, ring <NUM> is configured to seal against land <NUM> (i.e., the downstream face of groove <NUM>). As piston <NUM> and ring <NUM> move relative to each other, rubbing wear and friction may occur between the ring <NUM> and groove <NUM> (which includes land <NUM>). For example, without liquid lubricant (e.g., oil) present at this interface to reduce friction, galling could occur. To avoid galling and/or high friction between ring <NUM> and groove <NUM>, ring <NUM> may be included in the interface between ring <NUM> and groove <NUM>. <FIG> illustrates ring <NUM> arranged at the radially inner surface of ring <NUM>. In some embodiments, ring <NUM> may be arranged axially downstream of ring <NUM>. In some embodiments, ring <NUM> may be arranged in any suitable configuration relative to ring <NUM> such that it provides an intermediate sliding interface with desired wear properties between ring <NUM> and groove <NUM>.

<FIG> shows a cross-sectional view of illustrative device <NUM> including two free piston assemblies <NUM> and <NUM> that include respective sealing ringsets <NUM> and <NUM>, in accordance with some embodiments of the present disclosure. In some embodiments, device <NUM> may include linear electromagnetic machines <NUM> and <NUM> to convert between kinetic energy of respective free piston assemblies <NUM> and <NUM> and electrical energy. In some embodiments, device <NUM> may include gas regions <NUM> and <NUM>, which may, for example, be at a relatively lower pressure than gas region <NUM> (e.g., a high-pressure region) for at least some, if not most, of a cycle (e.g., an engine cycle, or an air compression cycle). For example, gas regions <NUM> and <NUM> (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 <NUM> and <NUM> are configured to provide reactants to, and remove exhaust from, bore <NUM> of cylinder <NUM>. In a further example, gas regions <NUM> and <NUM> may be vented to atmosphere (e.g., be at about <NUM> bar absolute pressure). In some embodiments, device <NUM> may include gas springs <NUM> and <NUM>, 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 <NUM> and <NUM> may each include respective pistons <NUM> and <NUM>, having grooves for respective sealing ring assemblies <NUM> and <NUM>, to seal respective gas regions <NUM> and <NUM> (e.g., high-pressure regions) from respective gas regions <NUM> and <NUM> (e.g., low-pressure regions).

Cylinder <NUM> may include bore <NUM>, centered about axis <NUM>. In some embodiments, free piston assemblies <NUM> and <NUM> may translate along axis <NUM>, within bore <NUM>, allowing gas region <NUM> to compress and expand. For example, gas region <NUM> may be at relatively high pressure as compared to gas region <NUM> for at least some of a stroke of free piston assemblies <NUM> and <NUM> (e.g., which may translate along axis <NUM> in opposed piston synchronization). Sealing ringsets <NUM> and <NUM> may seal gas region <NUM> from respective gas regions <NUM> and <NUM> within bore <NUM>. In some embodiments, free piston assemblies <NUM> and <NUM> may include respective pistons <NUM> and <NUM>, and respective sealing ringsets <NUM> and <NUM> which may be arranged in respective corresponding grooves of pistons <NUM> and <NUM>. It will be understood that gas regions <NUM> and <NUM>, and gas region <NUM>, may change volume as free piston assemblies <NUM> and <NUM> move or are otherwise positioned at different locations along axis <NUM>. The portions of respective sealing ringsets <NUM> and <NUM> nearest gas region <NUM> are each termed the front, and the portion of sealing ringsets <NUM> and <NUM> nearest respective gas regions <NUM> and <NUM> are each termed the rear. Sealing ringsets <NUM> and <NUM> may each include a high-pressure boundary, which may each depend on a pressure in gas region <NUM>. For example, a high-pressure boundary of sealing ringset <NUM> may be open to gas region <NUM> (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 <NUM> is unthrottled in the sealing ring assembly), or less than (e.g., if gas from gas region <NUM> is throttled in the sealing ring assembly), the pressure of gas region <NUM>. Sealing ringsets <NUM> and <NUM> may each include a low-pressure boundary, which may depend on a gas pressure in respective gas regions <NUM> and <NUM>. For example, a low-pressure boundary of sealing ringset <NUM> may be open to gas region <NUM> and have a corresponding pressure about the same as the pressure of gas region <NUM>.

In some embodiments, pistons <NUM> and <NUM> may each include one or more grooves into which one or more respective sealing ringsets may be arranged. For example, as shown in <FIG>, pistons <NUM> and <NUM> may each include one groove, into which sealing ringset <NUM> and sealing ringset <NUM> may be installed, respectively. In a further example, although not shown in <FIG>, piston <NUM> may include two grooves, in which two respective components of sealing ringset <NUM> may be installed. In a further example, piston <NUM> may include two grooves configured for a respective ring and applicator (not shown). A sealing ringset may be used to seal any suitable high pressure and low-pressure regions from each other. For example, sealing ringset <NUM> is configured to seal high-pressure region <NUM> (e.g., a gas spring) from low-pressure region <NUM>. In a further example, sealing ringset <NUM> is configured to seal high-pressure region <NUM> (e.g., a gas spring) from low-pressure region <NUM>.

In some embodiments, free piston assemblies <NUM> and <NUM> may include respective magnet sections <NUM> and <NUM>, which interact with respective stators <NUM> and <NUM> to form respective linear electromagnetic machines <NUM> and <NUM>. For example, as free piston assembly <NUM> translates along axis <NUM> (e.g., during a stroke of an engine cycle), magnet section <NUM> may induce current in windings of stator <NUM>. Further, current may be supplied to respective phase windings of stator <NUM> to generate an electromagnetic force on free piston assembly <NUM> (e.g., to effect motion of free piston assembly <NUM>).

In some embodiments, pistons <NUM> and <NUM>, sealing ringsets <NUM> and <NUM>, and cylinder <NUM> may be considered a piston and cylinder assembly. In some embodiments, device <NUM> 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 <NUM> need not include two free piston assemblies. For example, cylinder <NUM> could be closed (e.g., with a cylinder head), and free piston assembly <NUM> alone may translate along axis <NUM>.

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 engines and compressors. In some embodiments, the present disclosure is applicable to combustion and reaction devices such as a reciprocating engine and a free-piston engine. In some embodiments, the present disclosure is applicable to non-combustion and non-reaction devices such as reciprocating compressors, free-piston heat engines, and free-piston compressors. In some embodiments, the present disclosure is applicable to 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, chemical ignition (e.g., exposure to a catalytic surface, hypergolic ignition), plasma ignition (e.g., spark ignition), thermal ignition, any other suitable energy source for ignition, or any combination thereof. 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 such as waste heat or an external reaction such as combustion).

Claim 1:
A sealing ringset configured to seal against a bore (<NUM>) of a cylinder (<NUM>) without liquid lubricant, the sealing ringset comprising:
at least one sealing ring (<NUM>) configured to be arranged on a piston (<NUM>) to seal against the bore, characterized in that the at least one sealing ring is a metal ring; wherein said sealing ringset further comprises :
an applicator (<NUM>) comprising a solid lubricant configured to be arranged on the piston and to provide lubrication between the at least one sealing ring and the bore by wearing against the bore.