Patent Description:
For economic reasons, it is desirable for a seal of a piston-cylinder assembly to function for as long as possible before needing replacement. For example, a typical target might be hundreds or thousands of hours of operation. During these run hours the seal wears down radially, and gaps may form between portions of the seal. The total circumferential arc length of the resulting gap(s) opens by <NUM>*π*ΔR, where ΔR is the radial wear of the seal. With a self-lubricating material in which the wear rate is relatively high, the gap opens by an amount that results in unacceptable leakage flow, thus limiting the effective operating life of the seal. Accordingly, it would be desired for a seal to maintain performance during its lifetime. Surfaces of a seal may be exposed to a large range of pressures and contact forces. Similar sealing ring assemblies are known from <CIT>, <CIT>, and <CIT>.

In some embodiments, the present disclosure is directed to a sealing ring assembly. The sealing ring assembly includes a first sealing element having a first mating surface. The sealing ring assembly also includes a second sealing element having a second mating surface. The sealing ring assembly also includes a high-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element. The sealing ring assembly also includes a low-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element. At least one of the first mating surface and the second mating surface includes a recess open to the low-pressure boundary and not open to the high-pressure boundary, such that the first mating surface is sealed against the second mating surface by a first force acting on the first sealing element and a second force acting on the second sealing element.

In some embodiments, the first force acting on the first sealing element is directed opposite to the second force acting on the second sealing element.

In some embodiments, the recess is configured to cause the first and second forces to maintain a relative position of the first sealing element and the second sealing element.

In some embodiments, the first mating surface is sealed against the second mating surface in at least one of the radial, axial, and azimuthal direction. For example, the first and second surfaces may be flat, angled, curved, compound, or a combination thereof and may seal against each other in one or more directions at all, of or part of, the interface.

In some embodiments, the sealing ring assembly includes a rear axial face configured to seal against a land of a piston. In some embodiments, the sealing ring assembly includes a radially outer face configured to seal against a bore of a cylinder between the high-pressure boundary and the low-pressure boundary.

In some embodiments, the recess includes a groove.

In some embodiments, the recess is a first recess of the first mating surface, and wherein the second mating surface includes a second recess configured to interface with the first recess.

In some embodiments, the first sealing element includes a first ring segment, and the second sealing element includes a second ring segment.

In some embodiments, the first sealing element includes a ring segment, and the second sealing element includes a gap cover element.

In some embodiments, at least one of the first and second sealing elements includes a radial pressure-balancing feature configured to cause a radially inward force. For example, in some embodiments, the radially inward force reduces wear of the sealing ring assembly.

In some embodiments, the first and second mating surfaces seal against each other to prevent the recess from being open to the high-pressure boundary.

In some embodiments, the present disclosure is directed to a piston assemble including a piston and a sealing ring assembly. The piston includes a circumferential groove and the piston is configured to move axially within a bore of a cylinder. The sealing ring assembly is arranged in the circumferential groove and is configured to seal against the bore. The sealing ring assembly includes a first sealing element having a first mating surface and a second sealing element having a second mating surface. The sealing ring assembly also includes a high-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element, and a low-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element. At least one of the first mating surface and the second mating surface includes a recess open to the low-pressure boundary and not open to the high-pressure boundary such that the first mating surface is sealed against the second mating surface by a first force acting on the first sealing element and a second force acting on the second sealing element.

In some embodiments, the present disclosure is directed to a device including a cylinder, a piston, and a sealing ring assembly. The cylinder includes a bore having a high-pressure region and a low-pressure region. The piston includes a circumferential groove and the piston is configured to move axially within the bore. The sealing ring assembly is arranged in the circumferential groove and is configured to seal against the bore to define the high-pressure region and the low-pressure region. The sealing ring assembly includes a first sealing element having a first mating surface and a second sealing element having a second mating surface. At least one of the first and second mating surfaces includes a recess open to the low-pressure region and not open to the high-pressure region, such that the first mating surface is sealed against the second mating surface by a first force acting on the first sealing element and a second force acting on the second sealing element.

In some embodiments, the circumferential groove includes an axially rear land, and the sealing ring assembly is configured to seal against the axially rear land.

In some embodiments, the sealing ring assembly includes a radially outer face configured to seal against the bore.

In some embodiments, the sealing ring assembly includes a first boundary extending across at least a portion of the first sealing element and at least a portion of the second sealing element, and that is open to the high-pressure region. In some embodiments, the sealing ring assembly also includes a second boundary extending across at least a portion of the first sealing element and at least a portion of the second sealing element, and that is open to the low-pressure region, wherein the recess is open to the first boundary and not open to the second boundary.

In some embodiments, the present disclosure is directed to a sealing ring assembly including a first ring and a second ring. The first ring includes an extension extending axially rearwards, which includes a radially outward surface. The second ring includes an inner radial surface configured to interface to the radially outward surface. The sealing ring assembly also includes a groove extending circumferentially along at least one of the radially outward surface of the extension and the inner radial surface of the second ring. For example, the groove may be included in either or both of the first ring and the second ring.

In some embodiments, the groove is configured to be open to a low-pressure boundary of the sealing ring assembly.

In some embodiments, the second ring includes a pocket that extends circumferentially in an outermost radial surface of the second ring, and wherein the pocket is configured to receive high pressure gas. For example, the outermost radial surface is configured to seal against a bore of a cylinder.

In some embodiments, the second ring includes an orifice that is configured to allows gas to flow from the high-pressure boundary to the pocket. In some embodiments, for example, the second ring includes an orifice, slot, or other through feature.

In some embodiments, the sealing ring assembly is configured to be arranged in a ring groove of a piston. The sealing ring assembly includes an anti-rotation feature to prevent substantial azimuthal movement of the sealing ring assembly.

In some embodiments, the first ring includes an outermost radial surface, and wherein the outer radial surface of the extension is radially inward of the outer radial surface. For example, the outermost radial surface is configured to seal against the bore of the cylinder.

In some embodiments, at least one of the first ring and the second ring includes a self-lubricating material. For example, the first ring, the second ring, or both may include graphite or other ceramic, a polymer, or a combination thereof.

In some embodiments, the sealing ring assembly is configured for operation without liquid lubricant. For example, in some embodiments, the sealing ring assembly is configured for oil-less operation.

In some embodiments, the first ring includes at least two first ring segments, which are arranged such that respective ends of the at least two first ring segments form at least one interface between each other.

In some embodiments, the second ring comprises at least two second ring segments, which are arranged such that respective ends of the at least two second ring segments form at least one interface between each other.

In some embodiments, the present disclosure is directed to a piston assembly including a piston and a sealing ring assembly. The piston includes a ring groove. The sealing ring assembly is arranged in the ring groove and includes a first ring and a second ring. The first ring includes an extension extending axially rearwards, which includes a radially outward surface. The second ring includes radially inner surface configured to interface to the radially outward surface of the extension. The sealing ring assembly also includes a groove extending azimuthally along at least one of the radially outer surface of the extension and the inner radial surface of the second ring.

In some embodiments, the piston is an open-faced piston.

In some embodiments, the present disclosure is directed to a device including a cylinder, a piston, and a sealing ring assembly. The cylinder includes a bore. The piston includes a ring groove and is configured to travel within the bore along an axis of the bore. The sealing ring assembly is arranged in the ring groove and includes a first ring and a second ring. The first ring includes an extension extending axially rearwards, which includes a radially outward surface. The second ring includes an inner radial surface configured to interface to the radially outward surface. The sealing ring assembly also includes a groove extending azimuthally along at least one of the radially outer surface of the extension and the inner radial surface of the second ring.

In some embodiments, the sealing ring assembly is configured to seal between the bore and the piston. For example, the sealing ring assembly is configured to seal a high-pressure region in the bore from a low-pressure region in 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 ring assembly that is configured to separate a relatively higher-pressure region from a relatively lower-pressure region. The sealing ring assembly may include sealing elements such as, for example, one or more rings, one or more segments thereof, one or more gap covers, any other suitable components, or any combination thereof. There may be one or more surfaces of a first sealing element that must remain in contact (e.g., at an entire surface or any suitable portion thereof) with one or more corresponding surfaces of a second sealing element in order to sufficiently maintain sealing functionality. As the sealing ring assembly experiences wear, moves to accommodate changes in the cylinder diameter, or otherwise is subjected to geometric changes or changes in forces, some of the sealing elements may move relative to one another. In some embodiments, the present disclosure is directed to a pressure-locking feature that is configured to ensure that at least some of the mating surfaces of the sealing elements stay in contact to maintain a seal. For example, the mating surfaces may provide a seal between a high-pressure region and a low-pressure region. In an illustrative example, either or both of two mating surfaces include a channel or other recess that is open to the lower-pressure region. The geometry of the channel (e.g., area, volume, length, aspect ratio, surface-to-volume ratio) is such that the pressure acting on a portion of the mating interface is at a pressure lower than the pressure in the higher-pressure region. The surface in which the channel is included forms a continuous perimeter of contact with the mating surface (e.g., around the channel on all sides except in the location at which the channel is open to the lower-pressure region). For example, the channel does not create a significant short-circuiting flow path between the higher-pressure and lower-pressure regions (e.g., a leak). The particular fraction of the surface area exposed to the low-pressure channel is chosen such that the sum of pressure forces acting on the two segments (e.g. from the surfaces exposed to the higher-pressure region) has a net resultant force that causes the two segments to contact each other at the surfaces containing the pressure-locking feature. As such, the pressures and resulting contact forces to which the sealing ring assembly is exposed act to maintain the configuration of the sealing elements of the sealing ring assembly.

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, or 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 some 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 "gap cover element" shall refer to a sealing element configured to seal against one or more ring segments at an interface, and to seal against at least a portion of a bore during wear of the one or more ring segments. While a gap cover element may function as a ring segment as the ring wears, for purposes of the discussion in the present disclosure, a gap cover element is not considered to be a ring segment for purposes of clarity.

As used herein, a "sealing ring assembly" shall refer to an assembly of one or more rings, and sometimes also one or more gap covers elements, configured to engage with a piston and configured to seal between a high-pressure region and a low-pressure region of a cylinder. For example, a single ring segment may be a ring and a sealing ring assembly. In a further example, several ring segments and corresponding gap covers may be a sealing ring assembly.

As used herein, a "pressure-locking feature" shall refer to a feature included in at least one component of a sealing ring assembly that provides pressure locking functionality. As used herein, "pressure-locking" shall refer to the action of causing a resultant force on one or more components of a sealing ring assembly to maintain (or otherwise control) a relative geometric relationship between components of the sealing ring assembly, apply a force pushing components of the sealing ring assembly together, or both, during operation. The action of differential pressure across a sealing element may cause a resultant force that helps maintain the relative geometric relationship.

<FIG> shows a cross-sectional view of illustrative piston and cylinder assembly <NUM>, in accordance with some embodiments of the present disclosure. Cylinder <NUM> may include bore <NUM>, which is the inner cylindrical surface in which piston assembly <NUM> travels. Piston assembly <NUM> may include piston <NUM>, which includes a sealing ring groove <NUM>, in which sealing ring assembly <NUM> is configured to ride. As piston assembly <NUM> translates along the axial direction shown by axis <NUM> (e.g., during an engine cycle), in cylinder <NUM>, the gas pressure in high-pressure region <NUM> may change (high-pressure region <NUM> may be closed with a cylinder head or an opposing piston). For example, as piston assembly <NUM> moves opposite the direction of axis <NUM> (i.e., to the left in <FIG>), the pressure in high-pressure region <NUM> may increase. Low-pressure region <NUM>, located to the rear of sealing ring assembly <NUM> may be at a gas pressure below the pressure of high-pressure region <NUM> for at least some, if not most, of a piston stroke or cycle of piston and cylinder assembly <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. It will be understood that the "front" of sealing ring assembly <NUM> refers to the face axially nearest high-pressure region <NUM>, and the "rear" of sealing ring assembly <NUM> refers to the face 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).

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 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.

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.

In some embodiments, sealing ring assembly <NUM> may deposit material on bore <NUM> of cylinder <NUM> (e.g., include a self-lubricating material). Deposited material may lubricate the bore-to-sealing ring assembly interface between bore <NUM> and sealing ring assembly <NUM> (e.g., provide a dry lubricant). Accordingly, in some embodiments, piston and cylinder assembly <NUM> may operate without a liquid for lubrication (e.g., oil).

In some embodiments, piston <NUM> may be an open-faced piston. For example, piston <NUM> may include openings, cutouts, or other fluid paths from high pressure region <NUM> to ring groove <NUM>. Accordingly, in some embodiments employing an open-faced piston, the inner radial surfaces (e.g., referencing axis <NUM> in the radial direction in <FIG>) of sealing ring assembly <NUM> may be exposed to gas pressure of high pressure region <NUM>.

<FIG> shows a cross-sectional view of illustrative piston and cylinder assembly <NUM>, with a sealing ring assembly exposed to pressure forces, in accordance with some embodiments of the present disclosure. <FIG> shows a view directed azimuthally, with axis <NUM> directed in the radial direction, and axis <NUM> directed axially. Ring <NUM> and ring <NUM> constitute the sealing ring assembly, and each may include one or more ring segments. Although not shown in <FIG>, either or both of ring <NUM> and <NUM> may include one or more gap cover elements. The sealing ring assembly is arranged in groove <NUM> of piston <NUM> and is configured to seal against land <NUM>. While only pressure forces are illustrated in <FIG>, it will be understood that the sealing ring assembly may experience contact forces from a bore, a piston land, another sealing ring assembly, or a combination thereof. The sealing ring seals high-pressure region <NUM> from low-pressure region <NUM> against cylinder <NUM> (e.g., against a bore of cylinder <NUM>). Accordingly, the sealing ring assembly includes a high-pressure boundary exposed to high-pressure region <NUM> and a low-pressure boundary exposed to low-pressure region <NUM>. As illustrated in <FIG>, the sealing ring assembly is exposed to force <NUM> (i.e., directed axially rearward from high-pressure region <NUM>), force <NUM> (i.e., directed radially outwards from high-pressure region <NUM>), force <NUM> (i.e., directed radially inwards from pressure in a clearance gap between the sealing ring assembly and the cylinder <NUM>), and force <NUM> (i.e., directed axially forward from pressure in low-pressure region <NUM>). It will be understood that forces may be present in the azimuthal direction but are not shown in <FIG> for simplicity. Ring <NUM> includes recess <NUM>, which is coupled to low-pressure region <NUM> by passage <NUM>. Forces can also be applied at the interface between rings <NUM> and <NUM>. For example, if ring <NUM> and ring <NUM> are not accelerating relative to piston <NUM>, or each other, then the forces on each of ring <NUM> and <NUM> balance in all directions. Further description of interfacial forces is provided in the context of <FIG>.

<FIG> shows a cross-sectional view of a portion of an illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. As illustrated, only radial pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although axial pressure forces and axial and radial contact forces may be present during operation (e.g., from contact with a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that ring segments <NUM> and <NUM> do not move relative to one another). <FIG> shows a view directed azimuthally, with axis <NUM> directed in the radial direction, and axis <NUM> directed axially. Sealing ring assembly <NUM> includes a first ring and a second ring. The first ring includes ring segment <NUM>, and the second ring includes ring segment <NUM>. Sealing ring assembly <NUM> is configured to seal between high-pressure region <NUM> and low-pressure region <NUM> (e.g., in the bore of a cylinder). Force <NUM>, directed radially outward, is caused by pressure forces from high-pressure region <NUM> acting on a portion of a high-pressure boundary of the sealing ring assembly <NUM>. Force <NUM>, directed radially inward, is caused by pressure forces from a clearance gap, asperities, or both, between sealing ring assembly <NUM> and a cylinder bore. Force <NUM>, acting on ring segment <NUM>, is caused by gas pressure from gas of high-pressure region <NUM> in a gap between ring segments <NUM> and <NUM> (e.g., a similar force may act on ring segment <NUM> in the opposite direction). Resultant force <NUM> is the net radial force experienced by ring segment <NUM> from pressure forces during operation. For example, for a larger resultant force <NUM>, the larger the contact force from a bore (e.g., and increased wear rate) that may occur during operation.

<FIG> shows a cross-sectional view of a portion of an illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. As illustrated, only radial pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although axial pressure forces and axial and radial contact forces may be present during operation (e.g., from a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that ring segments <NUM> and <NUM> do not move relative to one another). <FIG> shows a view directed azimuthally, with axis <NUM> directed in the radial direction, and axis <NUM> directed axially. Sealing ring assembly <NUM> includes a first ring and a second ring. The first ring includes ring segment <NUM>, and the second ring includes ring segment <NUM>. Ring segment <NUM> includes recess <NUM>, arranged at an interface between ring segment <NUM> and ring segment <NUM>. Sealing ring assembly is configured to seal between high-pressure region <NUM> and low-pressure region <NUM> (e.g., in the bore of a cylinder). Force <NUM>, directed radially outward, is caused by pressure forces from high-pressure region <NUM> acting on a portion of a high-pressure boundary of the sealing ring assembly <NUM>. Force <NUM>, directed radially inward, is caused by pressure forces from a clearance gap, asperities, or both, between sealing ring assembly <NUM> and a cylinder bore. Force <NUM>, acting on ring segment <NUM>, is caused by gas pressure from gas in an interface between ring segments <NUM> and <NUM> (e.g., a similar force may act on ring segment <NUM> in the opposite direction). Because recess <NUM> is open to low-pressure region <NUM> by passage <NUM>, any high-pressure gas that gets into the interface between ring segments <NUM> and <NUM> is reduced in pressure, as illustrated by force <NUM> (e.g., with reduced magnitude from reduced pressure at recess <NUM>). For example, high-pressure gas that flows into gap will flow through recess <NUM> into passage <NUM> to low-pressure region <NUM>. Resultant force <NUM> is the net radial force experienced by ring segment <NUM> from pressure forces during operation and is less than resultant force <NUM> for similar operating conditions. For example, similar operating conditions may include pressures in high-pressure regions <NUM> and <NUM> being similar, and pressures in low-pressure regions <NUM> and <NUM> being similar. For example, for a smaller resultant force <NUM>, the smaller the contact force from a bore (e.g., and reduced wear rate) that may occur during operation. Accordingly, the inclusion of recess <NUM> allows sealing ring assembly <NUM> to experience a reduced resultant force from pressure forces (e.g., resultant force <NUM>) on a sealing element (e.g., ring segment <NUM>) as compared to a resultant force (e.g., resultant force <NUM>) acting on ring segment <NUM> of sealing ring assembly <NUM>.

A recess open to a low-pressure region may cause pressures at interfaces between sealing elements of a sealing ring assembly to be relatively lower (e.g., than if the recess were not included). For example, the pressure at the recess may, but need not, be equal to the pressure of the low-pressure region. The pressure being relatively less than that of the high-pressure region may be sufficient to provide pressure-locking. Accordingly, a recess need only cause the pressure to be reduced partially from the high-pressure region. For example, greater pressure reduction at the recess may provide stronger pressure locking (e.g., by reducing a resultant pressure force on the sealing element).

<FIG> shows a cross-sectional view of a portion of an illustrative sealing ring assembly <NUM> exposed to pressure and contact forces, in accordance with some embodiments of the present disclosure. <FIG> shows a view directed axially, with axis <NUM> directed in the radial direction, and arrow <NUM> illustrating the azimuthal direction. Ring segment <NUM> and gap cover element <NUM> constitute a portion of sealing ring assembly <NUM>, which may include any suitable number of ring segments, gap over elements, or other suitable components not illustrated in <FIG> (e.g., such as additional rings). Sealing ring assembly <NUM> is arranged in a groove of a piston and is configured to seal against a land. Sealing ring assembly <NUM> is configured to seal a high-pressure region from a low-pressure region of a cylinder (e.g., a bore thereof). As illustrated in <FIG>, the sealing ring assembly is exposed to force <NUM> (i.e., directed radially inward from pressure in a clearance gap), force <NUM> (i.e., directed radially outwards from a high-pressure region), force <NUM> (i.e., directed azimuthally from pressure), and force <NUM> (i.e., directed azimuthally opposite force <NUM> from pressure). It will be understood that forces may be present in the axial direction but are not shown in <FIG> for simplicity. Ring segment <NUM> includes recess <NUM>, which is coupled to a low-pressure region (not shown) by passage <NUM>. Forces can also be applied at the interface between ring segment <NUM> and gap cover element <NUM>. For example, if ring <NUM> and gap cover element <NUM> are not accelerating relative to the piston, or each other, then the forces on each of ring segment <NUM> and gap cover element <NUM> balance in all directions. Further description of interfacial forces is provided in the context of <FIG>.

<FIG> shows a cross-sectional exploded view of a portion of illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. As illustrated, only pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although contact forces may be present during operation (e.g., from a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that ring segment <NUM> and gap cover element <NUM> do not move relative to one another, a piston, or both). <FIG> shows a view directed axially, with axis <NUM> directed in the radial direction, and arrow <NUM> illustrating the azimuthal direction. Ring segment <NUM> and gap cover element <NUM> constitute a portion of sealing ring assembly <NUM>, which may include any suitable number of ring segments, gap over elements, or any other suitable components. Sealing ring assembly <NUM> is configured to be arranged in a groove of a piston and is configured to seal against a land. Sealing ring assembly <NUM> is configured to seal a high-pressure region from a low-pressure region of a cylinder (e.g., a bore thereof). Sealing ring assembly <NUM> is exposed to force <NUM>, which is directed radially inward from pressure in a clearance gap. Sealing ring assembly <NUM> is also exposed to force <NUM>, which is directed radially outwards (e.g., caused by gas from a high-pressure region). Sealing ring assembly <NUM> is also exposed to force <NUM>, which is directed azimuthally from pressure between a gap cover element (e.g., similar to gap cover element <NUM> of <FIG>) and ring segment <NUM>. Resultant force <NUM> is the net azimuthal force experienced by ring segment <NUM> from pressure forces during operation. For example, a larger resultant force <NUM> may reduce the effectiveness of the seal between ring segment <NUM> and gap cover element <NUM>, may increase wear of the sealing ring assembly <NUM>, or both.

<FIG> shows a cross-sectional exploded view of a portion of illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. Sealing ring assembly <NUM> is similar to sealing ring assembly <NUM> of <FIG>. As illustrated, only pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although contact forces may be present during operation (e.g., from a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that ring segment <NUM> and gap cover element <NUM> do not move relative to one another). <FIG> shows a view directed axially, with axis <NUM> directed in the radial direction, and arrow <NUM> illustrating the azimuthal direction. Ring segment <NUM> and gap cover element <NUM> constitute a portion of sealing ring assembly <NUM>, which may include any suitable number of ring segments, gap over elements, or any other suitable components. Sealing ring assembly <NUM> is configured to be arranged in a groove of a piston and is configured to seal against a land. Sealing ring assembly <NUM> is configured to seal a high-pressure region from a low-pressure region of a cylinder (e.g., a bore thereof). Sealing ring assembly <NUM> is exposed to force <NUM>, which is directed radially inward from pressure in a clearance gap. Sealing ring assembly <NUM> is also exposed to force <NUM>, which is directed radially outwards (e.g., caused by gas from a high-pressure region). Sealing ring assembly <NUM> is also exposed to force <NUM>, which is directed azimuthally from pressure between gap cover element <NUM> and ring segment <NUM>. Recess <NUM> in ring segment <NUM> is open to a low-pressure region (not shown), thus causing force <NUM> to be less than force <NUM> of <FIG>, for similar operating conditions. Resultant force <NUM> is the net azimuthal force experienced by ring segment <NUM> from pressure forces during operation. For example, a smaller resultant force <NUM>, relative to resultant force <NUM>, may aid in sealing between ring segment <NUM> and gap cover element <NUM> by increasing the contact force between their mating surfaces, may reduce wear of the sealing ring assembly <NUM>, or both.

<FIG> shows a cross-sectional view of illustrative piston and cylinder assembly <NUM>, with a sealing ring assembly (e.g., including rings <NUM> and <NUM>) exposed to pressure forces, in accordance with some embodiments of the present disclosure. <FIG> shows a view directed azimuthally, with axis <NUM> directed in the radial direction, and axis <NUM> directed axially. While only pressure forces are illustrated in <FIG>, it will be understood that the sealing ring assembly may experience contact forces from a bore, a piston land, another sealing ring assembly, or a combination thereof. Ring <NUM> and ring <NUM> constitute the sealing ring assembly, and each may include one or more ring segments. Although not shown in <FIG>, either or both of ring <NUM> and <NUM> may include one or more gap cover elements. The sealing ring assembly is arranged in groove <NUM> of piston <NUM> and is configured to seal against land <NUM>. The sealing ring seals high-pressure region <NUM> from low-pressure region <NUM> against cylinder <NUM> (e.g., against a bore of cylinder <NUM>). As illustrated in <FIG>, the sealing ring assembly is exposed to force <NUM> (i.e., directed axially rearward from high-pressure region <NUM>), force <NUM> (i.e., directed radially outwards from high-pressure region <NUM>), force <NUM> (i.e., directed radially inwards from pressure in a clearance gap between the sealing ring assembly and the cylinder <NUM>), and force <NUM> (i.e., directed axially forward from pressure in low-pressure region <NUM>). It will be understood that forces may be present in the azimuthal direction but are not shown in <FIG> for simplicity. Ring <NUM> includes recess <NUM>, which is coupled to low-pressure region <NUM> by passage <NUM>. Forces can also be applied at the interface between rings <NUM> and <NUM>. For example, if ring <NUM> and ring <NUM> are not accelerating relative to piston <NUM>, or each other, then the forces on each of ring <NUM> and <NUM> balance in all directions. Further description of interfacial forces is provided in the context of <FIG>.

<FIG> shows a cross-sectional exploded view of an illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. As illustrated, only axial pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although pressure forces in other directions and contact forces may be present during operation (e.g., from a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that ring <NUM> and ring <NUM> do not move relative to one another, relative to the piston, or both). <FIG> shows a view directed axially, with axis <NUM> directed in the radial direction, and arrow <NUM> illustrating the axial direction. Ring <NUM> and ring <NUM> constitute at least a portion of sealing ring assembly <NUM>, which may include any suitable number of ring segments, gap over elements, or any other suitable components. Sealing ring assembly <NUM> is configured to be arranged in a groove of a piston and is configured to seal against a land. Sealing ring assembly <NUM> is configured to seal a high-pressure region from a low-pressure region of a cylinder (e.g., a bore thereof). Ring <NUM> is exposed to force <NUM>, which is directed axially rearward and caused by gas in the high-pressure region. Force <NUM> from gas pressure between ring <NUM> and <NUM> acts on the mating surface of ring <NUM>. Resultant force <NUM> is the net axial force experienced by ring <NUM> from pressure forces during operation. For example, a smaller resultant force <NUM> may reduce the effectiveness of the seal between ring <NUM> and ring <NUM>. Forces <NUM> and <NUM> act on ring <NUM>, caused by pressure between rings <NUM> and <NUM>, and gas from the low-pressure region, respectively.

<FIG> shows a cross-sectional exploded view of an illustrative sealing ring assembly <NUM> exposed to forces, in accordance with some embodiments of the present disclosure. As illustrated, only axial pressure forces acting on sealing ring assembly <NUM> are shown in <FIG>, although pressure forces in other directions and contact forces may be present during operation (e.g., from a bore, a piston land, other sealing element, or other surface). For example, contact forces may have magnitudes and directions that balance the pressure forces in each direction (e.g., such that rings <NUM> and <NUM> do not move relative to one another). <FIG> shows a view directed azimuthally, with axis <NUM> directed in the radial direction, and axis <NUM> directed axially. Sealing ring assembly <NUM> includes a first ring (i.e., ring <NUM>) and a second ring (i.e., ring <NUM>). Ring <NUM> includes recess <NUM>, arranged at an interface between ring <NUM> and ring <NUM>. Sealing ring assembly is configured to seal between a high-pressure region and a low-pressure region (e.g., in the bore of a cylinder). Recess <NUM> is open to the low-pressure region by passage <NUM>. Ring <NUM> is exposed to force <NUM>, which is directed axially rearward and caused by gas in the high-pressure region. Force <NUM> from gas pressure between ring <NUM> and <NUM> acts on the mating surface of ring <NUM>. Resultant force <NUM> is the net axial force experienced by ring <NUM> from pressure forces during operation. For example, a larger resultant force <NUM> may improve the effectiveness of the seal between ring <NUM> and ring <NUM>. Forces <NUM> and <NUM> act on ring <NUM>, caused by pressure between rings <NUM> and <NUM>, and gas from the low-pressure region, respectively. Because recess <NUM> is open to the low-pressure region by passage <NUM>, any high-pressure gas that gets into the gap is reduced in pressure, as illustrated by resultant force <NUM> (e.g., with reduced magnitude from reduced pressure at recess <NUM>). For example, high-pressure gas that flows into the interface between rings <NUM> and <NUM> will flow through recess <NUM> into passage <NUM> to the low-pressure region. Resultant force <NUM> is the net axial force experienced by ring <NUM> from pressure forces during operation and is less than resultant force <NUM> of <FIG> for similar operating conditions. For example, similar operating conditions may include pressures in the high-pressure regions being similar, and pressures in the low-pressure regions being similar. For example, a larger resultant force <NUM> may improve the effectiveness of the seal between ring <NUM> and ring <NUM>, may improve wear of the sealing ring assembly, or both. Forces <NUM> and <NUM> act on ring <NUM>, caused by pressure between rings <NUM> and <NUM>, and gas from the low-pressure region, respectively.

It will be understood that <FIG> are merely illustrative, and that a sealing ring assembly may be configured to for axial, radial, or azimuthal pressure-locking, or any suitable combination thereof. For example, a sealing ring assembly may include one or more recesses, arranged at corresponding interfaces, configured to provide axial, radial, and azimuthal pressure-locking. Further, an interface between sealing elements may include any suitable shape (e.g., flat, segmented, contoured), and be arranged in any suitable direction (e.g., normal to, parallel to, or at an angle to any directional axis), or combination of directions. Any of the illustrative sealing ring assemblies of <FIG> may be combined or modified in accordance with present disclosure.

<FIG> shows an exploded perspective view of a portion of an illustrative sealing ring assembly, in accordance with some embodiments of the present disclosure. Sealing ring assembly <NUM> includes first ring <NUM> and second ring <NUM>. Although first ring <NUM> and second ring <NUM> are illustratively shown as having two segments and two splits, a ring may include any suitable number of segments and splits (e.g., one or more), in accordance with the present disclosure.

First ring <NUM> includes first ring segment <NUM> and second ring segment <NUM>. Additionally, first ring <NUM> may be referred to as a ring having two splits or being split into two ring segments. The first ring being "split" may refer to a fabrication process (e.g., the first ring is fabricated as a single part and separated into two ring segments), or the general geometry of first ring segments <NUM> and <NUM> arranged end to end and extending azimuthally around, wholly or partially, a ring groove of a piston. The split itself refers to the interface between first ring segments <NUM> and <NUM>, which may include a gap, contact between the first ring segments, or a combination thereof.

Second ring <NUM> includes second ring segment <NUM> and second ring segment <NUM>. Additionally, second ring <NUM> may be referred to as a ring having two splits or being split into two ring segments. Any suitable number of anti-rotation features may be included and may be configured to engage with any suitable number of corresponding features of a first or second ring, or segments thereof. In some embodiments, second ring <NUM> includes anti-rotation features <NUM> and <NUM> that engages with first ring <NUM>, or interfaces thereof, to prevent substantial azimuthal movement of second ring segments <NUM> and <NUM>.

First ring segments <NUM> and <NUM> may each include groove <NUM>, which extends circumferentially along an outer radial surface of extension <NUM>, which may also be split (e.g., as shown in <FIG>). Groove <NUM> may, for example, be open to a low-pressure boundary of sealing ring assembly <NUM> during operation. Accordingly, groove <NUM> may allow pressure-locking of sealing ring assembly <NUM> during suitable operation. For example, groove <NUM> may be configured to use a difference in pressure to lock (e.g., via pressure-locking) differing ring segments to one another (e.g., first ring segments <NUM> and <NUM> to ring segments <NUM> and <NUM>). As illustrated, groove <NUM> does not extend azimuthally along extension <NUM> to the interfaces between first ring segments <NUM> and <NUM> and thus will not be open to a high-pressure region during operation. <FIG> shows a perspective view of illustrative sealing ring assembly <NUM> of <FIG>, as assembly, in accordance with some embodiments of the present disclosure.

<FIG> shows a cross section view of illustrative sealing ring assembly <NUM> including a feature for pressure locking, in accordance with some embodiments of the present disclosure. Coordinate axes <NUM> (i.e., radial) and <NUM> (i.e., axial) are provided in <FIG> for purposes of clarity. Sealing ring assembly <NUM> is configured to be arranged in a ring groove of piston <NUM>.

The feature for pressure locking (i.e., groove <NUM>, as shown illustratively in <FIG>) may aid in maintaining sealing ring assembly <NUM> in an intended configuration during operation, which is referred to herein as pressure locking. During operation (e.g., in a device including a piston and cylinder assembly), groove <NUM> may be configured to include gas at a pressure close to a pressure of a low-pressure boundary of sealing ring assembly <NUM>. For example, during operation, groove <NUM> may achieve, or nearly achieve, a pressure of a low-pressure region (e.g., low-pressure region <NUM>) at the rear of sealing ring assembly <NUM>. Although groove <NUM> is illustrated as integral to front ring <NUM>, groove <NUM> could also be included in rear ring <NUM>, or both front ring <NUM> and rear <NUM>. Further, groove <NUM> may be replaced with any suitable recess configured to apply pressure to suitable faces of the sealing ring assembly. For example, a recess may include any suitable shape, having any suitable geometric properties, in accordance with the present disclosure.

To illustrate, in the absence of groove <NUM>, as the "twin ring" (e.g., sealing ring assembly <NUM>) wears, rear ring <NUM> may tend to wear at a faster rate than front ring <NUM>. This is due to the pressure dropping axially along the axial length of sealing ring assembly <NUM> (e.g., dropping from left to right as illustrated by the top arrows <NUM> pointing down). Accordingly, the pressure on the outside of the rear ring is lower than the peak pressure (e.g., in high-pressure region <NUM>). If high pressure gas gets between the front ring <NUM> and rear ring <NUM> (e.g., and thus exposes the rear segments of ring <NUM> to a pressure of high-pressure region <NUM>) rear ring <NUM> will then tend to be more strongly biased radially outwards than front ring <NUM>. As rear ring <NUM> wears at a greater rate, a gap between the rear ring segments will open. Gas from the high-pressure region then more easily gets between the segments, increasing the outward force, and a runaway condition may occur. Further, the flow of gas from high pressure region <NUM> into the gap may be characterized as leaking past the seal.

In some embodiments, a groove (e.g., groove <NUM>) is formed (e.g., cut) in one of the rings at the radial interface between front ring <NUM> and rear ring <NUM>. The groove may be included in the interface at the outer surface of front ring <NUM>, the inner surface of rear ring <NUM>, or both. In some embodiments, the groove is centered on, and open to, a split in rear ring <NUM>. The ends of groove <NUM> are closed before reaching the split in front ring <NUM> (e.g., as illustrated by groove <NUM> in <FIG>). When sealing ring assembly <NUM> is in operation (e.g., in a piston-cylinder device), the split in rear ring <NUM> is at low pressure because it is open to the rear of sealing ring assembly <NUM> and closed off from the front of sealing ring assembly <NUM>. Therefore, groove <NUM> between the two rings is also at low pressure, ensuring a low pressure between the front and rear segments which helps in them staying radially locked together.

Illustrative radial pressure fields <NUM> (i.e., acting radially inward) and <NUM> (i.e., acting radially outward) may act on sealing ring assembly <NUM> during operation. Radial pressure field <NUM> is directed radially outward and is created by gas from a high-pressure region acting on the radially inner surface of sealing ring assembly <NUM>. Radial pressure field <NUM> is directed radially inward and is created by gas in the clearance between sealing ring assembly <NUM> and a corresponding bore of a cylinder.

<FIG> shows a cross section view of illustrative sealing ring assembly <NUM> of <FIG> showing rear ring gap <NUM>, in accordance with some embodiments of the present disclosure. <FIG> is shown from section <NUM> of <FIG> (i.e., viewing in a direction radially inward, opposite the direction of axis <NUM>). Groove <NUM> is open to low-pressure region <NUM> and is sealed from high-pressure region <NUM> by the front ring <NUM>.

<FIG> shows a perspective view of a portion of illustrative sealing ring assembly <NUM> including a feature for balancing radial forces, in accordance with some embodiments of the present disclosure. <FIG> shows a perspective view of portion <NUM> of illustrative sealing ring assembly <NUM> of <FIG>, in accordance with some embodiments of the present disclosure. Sealing ring assembly <NUM> includes first ring <NUM> (e.g., a front ring) and second ring <NUM> (e.g., a rear ring). Second ring <NUM> includes pocket <NUM>, which extends circumferentially in an outer radial surface of the second ring. In some embodiments, pocket <NUM> is configured to receive high pressure gas (e.g., from a high-pressure region of a piston cylinder device). In some embodiments, second ring <NUM> may include orifice <NUM>, which may allow gas to flow from a high-pressure boundary of sealing ring assembly <NUM> (e.g., exposed to a high-pressure region) to pocket <NUM>. For example, orifice <NUM> may be open to pocket <NUM>, allowing the gas to flow. First ring <NUM> may include recess <NUM>, or other feature, to allow orifice <NUM> to receive high pressure gas during operation. Orifice <NUM> may include a hole, passage, or other opening which may allow suitable gas flow.

The portion of sealing ring assembly <NUM> shown by section <NUM> of <FIG>, viewed in direction <NUM>, is illustrated in <FIG>. Recess <NUM> in first ring <NUM> allows a relatively open flow path for high pressure gas to enter orifice <NUM>. Accordingly, in some circumstances, sealing ring assembly <NUM> may be configured to seal between a high-pressure region and a low-pressure region, and exhibit relatively lower wear (e.g., as compared to sealing ring assembly <NUM> of <FIG>) because of pocket <NUM> for radial pressure balancing. Under some circumstances, first ring <NUM> and second ring <NUM> may move azimuthally relative to one another as sealing ring assembly <NUM> wears. Accordingly, recess <NUM> may include a slot (e.g., as shown in <FIG>) rather than a circular hole, such that the pressurization pathway remains open as the ring wears.

<FIG> shows a view of the rear face of illustrative sealing ring assembly <NUM>, in accordance with some embodiments of the present disclosure. Sealing ring assembly <NUM> includes ring segments <NUM>, <NUM>, <NUM>, and <NUM>, as well as gap cover elements <NUM>, <NUM>, <NUM>, and <NUM>. Sealing ring assembly <NUM> illustratively corresponds to sealing ring assembly <NUM> after undergoing relatively less wear than sealing ring assembly <NUM> (e.g., ring segment <NUM> corresponds to ring segment <NUM> after undergoing an intermediate amount of wear).

Face <NUM> (e.g., axially forward of gap cover element <NUM> and facing axially rearward) of the interface between ring segments <NUM> and <NUM> is nominally a flat plane perpendicular to the axis of the ring. As shown in <FIG>, sides <NUM> of the interface between ring segments <NUM> and <NUM> are symmetric about a plane passing through the center of the radial split in the ring. The sides of gap cover elements <NUM>, <NUM>, <NUM>, and <NUM> need not be symmetric, but are shown symmetric for clarity. The sides together form an included angle (e.g., included angle <NUM> in <FIG> is formed by gap cover element <NUM>) that is widest at the radially inner surface of the ring and narrowest at the radially outer surface. The mating surfaces between gap cover element <NUM> and ring segments <NUM> and <NUM> may include at least one recess configured to be open to a low-pressure region and not open to (e.g., sealed from) a high-pressure region. For example, the recess may be included in sides <NUM>, front faces, corresponding mating surfaces of gap cover element <NUM>, or any combination thereof. Similarly, a recess may be included in any suitable sealing surface between any of illustrative ring segments <NUM>, <NUM>, <NUM>, and <NUM> and suitable gap cover elements <NUM>, <NUM>, <NUM>, and <NUM>.

<FIG> shows a cross-sectional view of illustrative device <NUM> including two free piston assemblies <NUM> and <NUM> that include respective sealing ring assemblies <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 ring assemblies <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 ring assemblies <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 ring assemblies <NUM> and <NUM> nearest gas region <NUM> are each termed the front, and the portion of sealing ring assemblies <NUM> and <NUM> nearest respective gas regions <NUM> and <NUM> are each termed the rear. Sealing ring assemblies <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 ring assembly <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 ring assemblies <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 ring assembly <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, as sealing ring assemblies <NUM> an <NUM> axially pass over respective ports <NUM> and <NUM> (e.g., and corresponding port bridges, although not shown), they may experience uneven, or reduced, inward force from bore <NUM>.

In some embodiments, pistons <NUM> and <NUM> 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>, pistons <NUM> and <NUM> may each include one groove, into which sealing ring assembly <NUM> and sealing ring assembly <NUM> may be installed, respectively. In a further example, although not shown in <FIG>, piston <NUM> may include two grooves, in which two respective sealing ring assemblies may be installed. In a further example, piston <NUM> may include two grooves, the first sealing ring assembly <NUM>, and the second (not shown), arranged to the rear of sealing ring assembly <NUM>, but with its front nearer to gas region <NUM>, thereby sealing pressure in gas region <NUM> to pressure between the two sealing ring assemblies (e.g., which may be less than pressure in gas region <NUM>). Accordingly, a sealing ring assembly may be used to seal any suitable high pressure and low-pressure regions from each other.

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 ring assemblies <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 ring assembly (<NUM>, <NUM>) comprising:
a first sealing element (<NUM>) comprising a first radially outward surface configured to seal against a bore of a cylinder, the first sealing element comprising a first mating surface; and
a second sealing element (<NUM>) comprising a second radially outward surface configured to seal against the bore of the cylinder, the second sealing element comprising a second mating surface; characterized in that said sealing ring assembly further comprises:
a high-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element; and
a low-pressure boundary extending across at least a portion of the first sealing element and across at least a portion of the second sealing element;
wherein at least one of the first mating surface and the second mating surface comprises a recess (<NUM>) open to the low-pressure boundary and not open to the high-pressure boundary, such that the first mating surface is configured to be sealed against the second mating surface by a first force acting on the first sealing element and a second force acting on the second sealing element.