Patent Description:
In a machine with a sealed oscillating rod, such as a Stirling- engine, -heatpump or - cryo-machine, there exists a high-pressure region within a cylinder separated from a relatively lower pressure region. Clearly, the high-pressure region must be sealed from the lower pressure region to maintain the pressure difference.

Generally, the piston rod must extend through the seal between the high-pressure region and the low-pressure region, resulting in the piston rod seal forming the primary seal between the high pressure and low-pressure regions.

The piston rod together with the rest of the crank drive is generally also lubricated. The lubrication may also improve the sealing at the piston rod seal; however, it is not desired that the lubrication enters the high-pressure region of the cylinder as this would lead to increased wear and reduced efficiency of the engine. The high-pressure region of the cylinder is nominally a dry region of the cylinder.

<CIT> discloses a piston rod seal comprising a gland with a tubular extension of slightly increasing diameter on the high-pressure side. The increasing diameter leads to a pumping effect at the part having the increased diameter during piston rod oscillation resulting in minimized oil transport to the high-pressure region of the cylinder. A disadvantage in sealing performance of such piston rod seals is, among other reasons, caused by the fact that piston rods move not only in their axial direction, they also move orthogonally/laterally due to some play in the guiding crosshead and piston guide. Reasons are friction and constrains between the seal and its support with respect to the rod seal housing. The limited movability of the annular seal laterally to the rod results in misalignment and allows some leaking of lubrication oil and gas.

<CIT> discloses an a sealing system for restricting fluid flow around a piston rod between a piston cylinder and crankshaft space in a hot gas engine. A seal element is secured around the piston rod in an intermediate chamber, including a link in the crankshaft space connecting, and permitting relative radial motion between, the piston rod and the crosshead and an O-ring having a diameter substantially greater than that of the piston rod and being secured between a lower ring securing the seal element in place around the piston rod and a wall of the intermediate chamber for frictionally restricting radial movement of the lower ring.

Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above-mentioned problems by providing a rod seal assembly for a machine comprising a crosshead and a sealed oscillating piston rod according to claim <NUM>. The proposed rod seal assembly provides an improved lateral following of the rod seal and it's supporting parts to the piston rod. The rod seal assembly comprising:
a seal housing, a rod seal, a bushing and a rod seal base wherein the rod seal, the bushing and the rod seal base are annular and can be laterally moved in relation to the seal housing. The housing axially supports the rod seal base and it is adapted to be arranged around the piston rod and provided with a base portion. The base portion comprises a lower axial surface, directed in a first axial direction, and an upper axial surface, directed in a second axial direction. The lower axial surface abut the housing and the upper axial surface is provided with a rod seal seat. The rod seal is adapted to be arranged around the piston rod and has a first end portion and a second end portion. The first end portion is arranged to connect to the rod seal base in the first axial direction, and the bushing is arranged to abut the rod seal in the first axial direction, and the rod seal base and the bushing are arranged to have an axial overlap. An inner seal ring is arranged between lower axial surface of the base portion and the seal housing. An outer seal ring is arranged between the lower axial surface of the base portion and the seal housing, wherein the outer seal ring is arranged radially outside the inner seal ring, and the lower surface of the base portion is provided with an annular slot defined by at least one radial inner wall at which the inner seal ring is arranged and an outer radial wall at which the outer seal ring is arranged, and the base portion further comprising a pressure relief channel arranged to connect the lower and the upper axial surfaces of the base portion.

One exemplary effect of the axial overlap is that the bushing can be aligned with the rod seal base, whereby the lateral movement of the piston rod which is transferred to the rod seal also is transferred to the base and further to the bushing, whereby all lateral movable parts are aligned through the rod seal contact with the piston rod. Aligning all lateral movement of the rod seal assembly reduces the wear of the rod seal assembly.

The rod seal can be provided with an internal diameter which tapers outward towards its upper portion such that it has an internal diameter at its upper portion, which is greater than the external diameter of the piston rod and greater than the internal diameter of its lower portion.

The rod seal base and the rod seal can be integral parts or be separate parts abutting each other. In one exemplary embodiment the rod seal base and the rod seal are separate parts, whereby the rod seat base is provided with a conical seat adapted to receive a correspondently conical first end portion of the rod seal.

In one exemplary embodiment the rod seal is made of a soft seal material in order to be able form a tight seal towards any abutting surfaces. Exemplary materials are PTFE, PEEK, PI and compounds thereof, Nitrile, Neoprene, EPDM, rubber, fluorocarbon and silicone.

In one exemplary embodiment the rod seal base is made of a rigid material, such as a metal or a polymer or a composite material. The bushing is made of a material with at least a rigidity allowing it to transfer the needed axial forces upon the rod seal.

In one exemplary embodiment of the overlap, the axial overlap is formed by the bushing extending in the first axial direction towards the rod seal base at least partially past where the bushing abuts the rod seal.

In one exemplary embodiment of the overlap, the axial overlap is formed by that the rod seal base extends in the second axial direction towards the bushing at least partially past where the rod seal base abuts the rod seal.

In one exemplary embodiment of the overlap, the rod seal base and the bushing have a radial contact at the axial overlap. The radial contact is preferably constructed with a minimal of play, whereby one exemplary effect thereof is that a lateral alignment between is maximised.

In another exemplary embodiment, the rod seal comprises a shoulder portion, and the bushing comprises a corresponding shoulder portion arranged to mate with the shoulder portion of the rod seal.

In one exemplary embodiment, the shoulder portions are corresponding conical shoulder portions such that a radial force is applied to the rod seal toward the piston rod.

In one exemplary embodiment of the rod seal, the shoulder portion of the rod seal is provided with a secondary seal ring. The secondary seal ring is adapted to seal between the bushing and the rod seal seat.

In one exemplary embodiment of the rod seal assembly, at both axial sides of the base portion of the rod seal base, the seal housing extends radially inwards relative an outer periphery of the base of the rod seal base. The seal housing thereby at least partially encloses the rod seal base on both axial sides. One exemplary effect thereof is that equalising pressure surfaces can be created upon the rod seal base, which pressure surfaces can reduce the friction between the rod seal base and the housing.

In another exemplary embodiment of the rod seal assembly (not claimed), an inner seal ring is arranged between lower surface of the base and the seal housing. A seal ring is normally arranged in a slot to be arranged at a specific radial distance from a centre axis (in this case the axis of the piston rod). The slot can be provided in either the housing or the lower surface of the base. One exemplary advantage by providing an inner seal ring is that an inner region with reduced diameter is formed by the inner seal ring. The inner region forms an inner wet part that is lubricated, whereby also an outer (radial outside the inner seal ring) dry part that is not lubricated is created. The reduced and lubricated diameter results in less friction and wear between the rod seal base and the seal housing during lateral movement therebetween, is achieved.

In an embodiment of the rod seal base according to the invention, the lower surface of the base is provided with an annular slot, wherein the annular slot is defined by at least one radial inner wall at which the inner seal ring is arranged. The annular slot can be open, i.e. not having an outer radial wall, or at least partially closed, i.e. be provided with an outer radial wall. One exemplary effect with an open slot is that the only attachment point between the rod seal base and the housing is the lubricated area between the inner seal and the piston rod.

In an embodiment of the rod seal assembly according to the invention, an outer seal ring is arranged between the lower surface of the base and the seal housing, wherein the outer seal ring is arranged radially outside the inner seal ring.

In one exemplary embodiment of the rod seal base, the annular slot comprising an outer radial wall and the outer seal ring is arranged at the outer radial wall.

When an inner and an outer seal ring are provided between the rod seal base and the housing, they are provided in the same annular slot. If the same annular slot is used, the annular slot can have radial extension such that a space is created between the inner seal ring, the outer seal ring, the rod seal base and the housing.

A corresponding space can be created also when separate annular slots are used (not claimed), by adjusting the distance between the rod seat base and the housing in between the two annular slots/the inner and outer seal ring.

In an embodiment of the rod seal base according to the invention, the base further comprises a pressure relief channel arranged to connect the lower and the upper axial surfaces of the base.

In one exemplary embodiment of the rod seal assembly, it further comprises an upper seal ring provided between the upper axial surface of the rod seal base and the seal housing and the pressure relief channel mouth at the lower axial surface radially between the inner and outer seal ring and mouth at the upper axial surface radially inside the upper seal ring.

One exemplary effect of the pressure relief channel is that it equalises the pressure of the upper surface (directed in the second radial direction) of the rod seal base and the lower surface (directed in the first axial direction) of the rod seal base, i.e. the lower axial surface between the inner and outer seal ring are subjected to the high pressures from inside the compression chamber. One exemplary effect thereof is that by adjusting the axial surfaces subjected to the pressure of the high pressure side, such that the resulting pressure force is essentially zero, a reduced axial normal force can be achieved upon the rod seal base, wherein less friction and wear between the rod seal base and the seal housing during lateral movement therebetween is achieved.

In one exemplary embodiment of the rod seal assembly, an outer diameter of the upper seal ring is less than an outer diameter of the outer seal ring. An effect exemplary effect thereof is that a pressure force equilibrium can be created.

In one exemplary embodiment of the rod seal base, an upper axial surface of the rod seal base being radially inside the upper sealing and radially outside the outer sealing is essentially equal to the lower axial surface of the rod seal base radially inside the inner sealing. One exemplary effect thereof is that a pressure equilibrium that reduces friction between the rod seal base and the housing is achieved.

In one exemplary embodiment of the rod seal base, the lower axial surface of the base portion varies in axial extension such that it only abuts the seal housing radially outside the outer seal ring. radially inside the inner seal ring the rod seal base extends less in the first axial direction than radial outside the outer seal ring, whereby the base portion only abuts the seal housing radially outside the outer seal ring.

In one exemplary embodiment, the housing is provided with a channel extending from an ambient side outside of the rod seal assembly and into the rod seal assembly at a position in the proximity of and radially outside the outer seal ring. One exemplary effect thereof is that an ambient pressure is ensured the outside of the outer seal ring. Additionally, if the channel extends from the proximity of the opening for the piston rod, a lubrication of the lower surface of the rod seal base outside the outer seal can be achieved through the channel.

In one exemplary embodiment of the rod seal assembly, the rod seal base comprising a lateral bearing arranged to allow a lateral displacement of the rod seal base and the seal housing. One exemplary effect is that the lateral bearing can take up the lateral movement of the rod seal base, without a minimal friction between the parts and thereby minimal wear.

In one exemplary embodiments of the lateral bearing, the lateral bearing comprises a plurality of bearing rods extending from the housing in a first axial direction towards the rod seal base, which is suspended in the bearing rods. In one exemplary embodiment of the lateral bearing, a plurality of laterally flexible rods arranged to abut the housing in a first axial direction from the rod seal base. In one exemplary embodiment of the lateral bearing, it comprises a circular ball bearing and in another exemplary embodiment it comprises a laminated bearing, which comprises a plurality of flexible polymer layers between rigid layers. The lateral flexibility is relative the forces applied in the application.

In one exemplary embodiment of the rod seal assembly, the rod seal assembly is provided with a gas-permeable covering in proximity of the first end portion of the rod seal, wherein the covering is annular and guided by the bushing such that it follows lateral movements of the bushing. One exemplary effect of the covering is that it stops dirt to from entering the interior of the rod seal assembly and thereby minimises wear.

In another exemplary embodiment of the rod seal assembly, the rod seal assembly further comprises at least one spring member arranged to apply an axial force, in the first axial direction, to the rod seal via the bushing. One exemplary effect thereof is that the bushing can maintain a force acting on the rod seal and thereby secure a tight seal against the piston rod.

In one exemplary embodiment of the spring member, the spring member is arranged radially outside the rod seal and at least partially axial outside the bushing and at least partially at the same axial height as the bushing. One exemplary effect of providing the spring member radial outside the main parts of the rod seal is that the lateral movement of the bushing is not affected by the spring member. In one exemplary embodiment the spring member is an extension spring. One exemplary effect of providing an extension spring is that it does not buckle.

In another exemplary embodiment of the spring member, the bushing is provided with a radial flange wherein the at least one spring member is arranged radially outside of the bushings main body and extends between the flange and the seal housing.

One aspect of this disclosure concerns a machine comprises a crosshead, a sealed oscillating piston rod and a rod seal assembly according to any of the embodiments disclosed herein.

In one exemplary embodiment of the machine, the machine is a stirling engine.

Further advantageous embodiments are disclosed in the appended and dependent patent claims and in the below discussed drawings.

These and other aspects, features and advantages of which the invention is capable will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying schematic drawings, in which.

The present disclosure relates to a piston rod seal assembly <NUM> for a machine <NUM> (<FIG>) with crosshead <NUM> and a sealed oscillating piston rod <NUM> with a rod seal <NUM>. The machine is typically a hot gas machine, e.g. a sterling engine comprising a compression <NUM> and an expansion cylinder <NUM>. The compression cylinder <NUM> is provided with a rod seal assembly <NUM> according to any embodiment disclosed herein. The rod seal assembly <NUM> seals a high-pressure HP region in a cylinder from a low-pressure region LP. The low-pressure LP region has normally an ambient pressure. The rod seal assembly <NUM> furthermore seals and limits the ingress of lubricant into the high-pressure HP region of the cylinder. The rod seal assembly <NUM> disclosed herein results in reduced wear of the rod seal assembly <NUM> during of lateral movement of the piston rod <NUM>, due to improved lateral following of the rod seal <NUM> and its supporting components, e.g. rod seal base <NUM>, bushing <NUM>, spring <NUM>, with reduced wear on the rod seal assembly <NUM> components. Additional effects are thereby reduced leakage between the high-pressure HP and the low-pressure region as well as between the dry and the wet region, which essentially corresponds to the high pressure and low-pressure regions.

<FIG> discloses an exemplary embodiment of a piston rod seal assembly <NUM> (not claimed).

The rod seal assembly <NUM> is provided in a cylinder <NUM> and comprises an annular rod seal <NUM> arranged around a piston rod <NUM>. The rod seal <NUM> has a lower partial conical portion <NUM>. That is, the lower portion of the rod seal <NUM> has a tapered external surface tapering inwardly toward its center, and thereby toward the piston rod <NUM>. The lower conical portion <NUM> is arranged to contact a separate annular rod seal base <NUM>. The rod seal base <NUM> and the rod seal <NUM> are provided within a seal housing <NUM>. The rod seal base <NUM> seals between the seal housing <NUM> and the rod seal <NUM>. The seal housing <NUM> has a passage <NUM> through which the piston rod <NUM> can be arranged and in which it oscillates. The seal housing <NUM> can furthermore form an enclosure or a partial enclosure for the rod seal assembly <NUM>. The seal housing <NUM> can also be called seal plate <NUM>.

An exemplary embodiment of the rod seal <NUM> has an internal diameter which tapers outward towards its upper portion <NUM> such that it has an internal diameter slightly larger than the external diameter Dp of the piston rod <NUM> at its upper portion <NUM>. the upper internal diameter Du at the upper portion <NUM> of the rod seal <NUM> is larger than the lower internal diameter Dl of the lower conical portion <NUM> of the rod seal <NUM> and the upper internal diameter Du is thereby larger than the external diameter Dp of the piston rod <NUM>, which is essentially equal to the lower internal diameter Dl.

The sealing ring <NUM> can also called a rod seal seat <NUM> or a rod seal base <NUM>.

In one exemplary embodiment, the rod seal <NUM> and the rod seal base <NUM> forms one integral part. The rod seal base <NUM> thereby forms a lower portion of the rod seal <NUM>, as exemplary disclosed in <FIG>. One exemplary effect thereof is that less individual parts are needed in the rod seal assembly <NUM>.

In the embodiments disclosed in <FIG>, <FIG> and <FIG> and <FIG> the rod seal base <NUM> and the rod seal <NUM> are separate parts and the rod seal base <NUM> has a conical seat <NUM>. The embodiments disclosing separate rod seal <NUM> and rod seal base <NUM> are interchangeable with the integral rod seal <NUM> and rod seal base <NUM>.

Now, in the embodiment disclosed in <FIG>, the conical seat <NUM> of the rod seal base <NUM> forms a conical seat for the rod seal <NUM>. The piston rod <NUM>, the rod seal <NUM>, and the rod seal base <NUM> may all move laterally with respect to the seal housing <NUM>. The rod seal base <NUM> is fixed laterally with respect to the piston rod <NUM>. Compared to existing solutions the provision of the rod seal base <NUM> enables the piston rod <NUM> and rod seal <NUM> to move laterally and maintain sealing performance. This is because the rod seal <NUM> is not held with respect to the seal housing <NUM> but is rather free to move, at least slightly, laterally with lateral movements of the piston rod <NUM>.

To maintain the lower conical portion <NUM> of the rod seal <NUM> within the rod seal base <NUM> a force is applied to the rod seal <NUM> toward the sealing ring <NUM>. The force is an axial force, that is, it acts in the direction of the longitudinal extension of the rod seal <NUM>. The force may be provided by a spring <NUM>. The spring <NUM> may apply a force to a bushing <NUM> which is arranged around the rod seal <NUM>. The bushing <NUM> may apply an at least axial force to the rod seal <NUM>. The bushing <NUM> has a portion <NUM> for contacting the rod seal <NUM>. The bushing <NUM> may be an annular bushing provided with an external shoulder <NUM> at its lower portion. The external shoulder <NUM> forms a seat for the lower portion of the spring <NUM>. The spring <NUM> may be arranged around the bushing <NUM>. The spring <NUM> may be radially outside the bushing <NUM>. That is, the rod seal <NUM> may be within the bushing <NUM>, the spring <NUM> may be outside the bushing <NUM>. Alternatively, the axial force may be provided by an inherent springing capacity in a bushing <NUM>.

As disclosed in all the disclosed embodiment of the rod seal assembly <NUM>, the rod seal base <NUM> and the bushing <NUM> has an axial overlap <NUM> at which they have a radial contact, such that the bushing <NUM> is guided by the rod seal base <NUM>, i.e. the bushing <NUM> is laterally aligned with the rod seal base <NUM>. An exemplary effect thereof is that the bushing <NUM> always follows the lateral movement of the rod seal base <NUM>.

Although not shown in the figures, the conical seat <NUM> and the lower conical portion <NUM> of the rod seal <NUM> may instead be flat, laterally extending portions forming a pair of mating surfaces. That is, the pair of mating surfaces extend at an angle of <NUM>° to the longitudinal axis of the rod seal <NUM> and/or piston rod <NUM>. In such an arrangement there is no radial force applied by the sealing ring <NUM> to the rod seal <NUM> or vice-versa. The sealing ring <NUM> and the rod seal <NUM> apply only an axial force, in line with the longitudinal axis of the rod seal <NUM> to each other.

Embodiments where the rod seal <NUM> and the rod seal base <NUM> are integral are disclosed in <FIG>. The rod seal <NUM> comprises a lower portion being the sealing ring <NUM>.

A partial enlargement of the rod seal assembly <NUM> of <FIG> is disclosed in <FIG>. The internal wall of the bushing <NUM> may be provided with an internal shoulder portion <NUM> which may be arranged to interact with a corresponding shoulder portion <NUM> of the lower portion of the rod seal <NUM>. The shoulder portion <NUM> of the lower portion of the rod seal <NUM> may be a conical portion which tapers radially outward, that is, away from the piston rod <NUM>. If the shoulder portion <NUM> of the lower portion of the rod seal <NUM> is a conical tapered portion, then the internal shoulder portion <NUM> of the bushing <NUM> is a corresponding conical portion, such that the surfaces mate. That is, the internal tapered portion <NUM> of the bushing <NUM> may be arranged to abut with the upper conical portion <NUM> of the lower portion of the rod seal <NUM>. The corresponding conical portions result in an axial force being applied to the rod seal <NUM> toward the piston rod <NUM>. The internal shoulder portion <NUM> and the shoulder portion <NUM> may also be flat, that is, not tapered. The flat surfaces extend laterally outward from the longitudinal axis of the rod seal <NUM>. A flat surface, lacking conical tapers as described above, does not apply any lateral/radial force to the rod seal <NUM>. A force applied by the spring to the bushing <NUM> applies a force to the rod seal <NUM> to maintain it in position within the rod seal base <NUM>. The lower portion of the bushing <NUM> may be provided with a lip <NUM> which extends past the upper shoulder portion <NUM> of the lower portion of the rod seal <NUM> such that the rod seal is substantially enclosed within the bushing <NUM>. The lip <NUM> may have an internal diameter which is greater than the internal diameter of the upper portion of the bushing <NUM>. The lip may extend in the first axial direction AD1 such that it forms the overlap <NUM> to the rod seal base <NUM>. The cylindrical outer surface <NUM> of the lip <NUM> may be guided in the cylindrical bore <NUM> of the rod seal housing <NUM> to secure that the spiral spring <NUM> limit buckling of the spring <NUM> which would tilt the bushing <NUM> and apply a lateral radial force to the rod seal <NUM>. However, if the rod seal assembly <NUM> is displaced laterally the compression spring <NUM> as shown in <FIG> and <FIG> may, in some instances, nevertheless buckle and the lip <NUM> will not allow lateral movement of the bushing due to its guiding function. As the bushing <NUM> cannot move laterally more than the play between the lip <NUM> and the rod seal housing allows, the lateral movement of the rod seal is limited. The lip <NUM> does however snuggly fit at the overlap <NUM> to the rod seal base <NUM>, such that the bushing <NUM> is guided thereby.

A secondary seal ring <NUM> may be provided between the upper <NUM> and lower <NUM> conical portions of the rod seal <NUM>. The secondary seal ring <NUM> may be for example an O-ring or a similar gasket. The secondary seal ring <NUM> may seal between the rod seal <NUM>, the bushing <NUM> and/or the seal seat <NUM>.

The rod seal base <NUM> is arranged on an internal base <NUM> of the seal housing <NUM>. The rod seal base <NUM> is provided with an annular slot <NUM>. The annular slot <NUM> may be provided with a compliant sealing ring seal <NUM>, for example, an O-ring or similar gasket. The annular slot may house the sealing ring seal <NUM>. The sealing ring seal <NUM> may at least partially form a seal separating the nominally dry part of the cylinder, from the nominally lubricated part of the cylinder. The annular slot <NUM> is disclosed to be formed in the rod seal base <NUM>, but can equivalent be formed in the base <NUM> of the seal housing <NUM>.

The seal housing <NUM> seals against the wall of the cylinder <NUM>. The radial perimeter <NUM> of the seal housing <NUM> may be provided with an annular slot <NUM>. The annular slot <NUM> may house a seal <NUM>, for example, an O-ring, or similar gasket, which seals the seal housing against the wall of the cylinder <NUM>.

A covering <NUM> may be provided above the rod seal <NUM> to seal against ingress of particles to the lubricant on the piston rod <NUM>. The covering <NUM> is arranged distal the rod seal base <NUM>. That is, the covering <NUM> is at the opposite end of the rod seal assembly <NUM> to the rod seal base <NUM>. The covering <NUM> encloses a region comprising at least the rod seal <NUM>. The covering <NUM> may be gas-permeable such that it does not form a gas-tight seal. The covering <NUM> may be an annular member which is arranged between the bushing <NUM> and a washer <NUM> arranged on top of the covering <NUM>. A washer <NUM> is fixed in the seal housing <NUM> such that it the cover <NUM> is held in place above the rod seal <NUM>. The covering <NUM> may, for example, be an annular covering with a central aperture for the piston rod <NUM>. The covering may comprise, such as be composed of, a non-woven textile such as a felt or similar. The non-woven textile has the advantage that it is gas-permeable and absorbs particle matter which may enter the lubricant. The non-woven textile may also partially absorb lubricant. The particle matter present may be metal worn from the piston, piston rings, and other components in the Stirling engine.

To further reduce friction between the seal housing <NUM> and the rod seal base <NUM> the slot <NUM> of the rod seal base <NUM> may be open at its outer diameter, as disclosed in <FIG> and <FIG>. That is, the slot <NUM> may extend to the radial outer wall of the rod seal base <NUM>. The open slot <NUM> results in a rod seal base <NUM> having an annular recess around its base portion. The annular recess forms a region of reduced external diameter at the base of the rod seal base <NUM>. Minimizing friction between the rod seal base <NUM> and the seal housing <NUM> results in reduced wear on the rod seal <NUM>, seal housing <NUM> and piston rod <NUM>. The open annular slot <NUM> results in surface contact between the seal housing <NUM> and the rod seal base <NUM> only at the lubricated portion of the rod seal assembly <NUM>. There is no contact at the nominally dry part of the cylinder which reduces wear.

To further reduce friction between the seal housing <NUM> and the rod seal base <NUM>, the rod seal base <NUM> may be coated with a low friction coating such as diamond-like carbon (DLC) or polytetrafluoroethylene (PTFE) or similar coating. The low-friction coating may be combined with the open slot <NUM> described above or any other friction reducing measure described herein. Alternatively, or combined the internal base <NUM> of the housing <NUM> can be covered with the same or similar low friction coating.

To further improve the lateral mobility of the rod seal assembly <NUM>, and therefore reduce friction and wear on the components of the rod seal assembly <NUM> the rod seal base <NUM> may comprise an upper portion with a cylindrical aligning wall <NUM> as shown in the embodiments disclosed in e.g. <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG>.

<FIG> discloses rod seal base <NUM> having a cylindrical wall <NUM> extending longitudinally from the perimeter of the bottom portion of the rod seal base <NUM> in the second axial direction AD2. The cylindrical wall <NUM> extends coaxially with the rod seal <NUM>, and piston rod <NUM>. In the embodiment disclosed in <FIG> (not claimed), the rod seal base <NUM> comprises a conical seat <NUM>. The conical seat <NUM> forms a seat for the rod seal <NUM>. As described above, the conical seat <NUM> and the rod seal <NUM> may also be flat, such that they form a pair of laterally extending mating surfaces. The cylindrical wall <NUM> forms an aligning wall partially surrounding the bushing <NUM>, and thereby forming the overlap <NUM>, securing that the bushing <NUM> can follow lateral movements of the rod seal <NUM> and rod seal base <NUM>. The cylindrical aligning wall <NUM> may surround the bottom portion of the bushing <NUM> or extend further upwards in the second axial direction. The cylindrical aligning wall <NUM> may surround the bottom portion of the rod seal <NUM>. As previously described, to keep the rod seal <NUM> in place, the rod seal <NUM> is forced towards the rod seal base <NUM> through an axial force Fs. The bushing <NUM> is arranged to surround the upper portion of the rod seal <NUM>. The axial force Fs can be introduced through inherent resilient capacity of the bushing <NUM> or as disclosed in <FIG> by a spring <NUM>.

As described above, in some exemplary embodiments the rod seal base <NUM> and the rod seal <NUM> may be integral. In such an arrangement, the lower portion of the bushing <NUM> is arranged radially between the upper portion of the rod seal <NUM> and at least a portion of the cylindrical wall <NUM>.

The base portion <NUM> of the rod seal base <NUM> may be provided with the open annular slot <NUM> as described above. The seal <NUM>, such as an O-ring may be provided at the open annular slot <NUM>. The seal <NUM> seals the lubricated side of the seal assembly <NUM> from the non-lubricated, or dry side. As described above, the rod seal base <NUM> may sit on the internal base <NUM> of the seal housing <NUM>.

A covering <NUM> may be provided above the rod seal as disclosed above. The covering may be gas permeable. It may comprise, such as be composed of a non-woven material which can prevent particles from entering the lubricant. The covering <NUM> may be arranged to be held in place by the bushing <NUM>, and/or the rod seal <NUM>. The covering <NUM> may move laterally with the piston rod <NUM>, rod seal <NUM>, bushing <NUM>, and/or rod seal base <NUM>. The covering <NUM> is disclosed in the embodiments disclosed in <FIG>, <FIG>, <FIG> and <FIG>.

All embodiments of the rod seal assembly <NUM> disclosed, comprises at least one spring <NUM> provided to apply the force to the bushing <NUM>, which applies a force at the rod seal <NUM> towards the rod seal base <NUM>. In some exemplary embodiments of the spring <NUM>, the at least one spring <NUM> may be extension spring as shown in <FIG>, <FIG>, <FIG>, and <FIG>. The at least one spring may be connected at a first end <NUM> to a flange <NUM> provided on an upper portion of the bushing <NUM>. The flange <NUM> is an annular lateral flange extending around the upper portion of the bushing <NUM>. The at least one spring <NUM> may be connected at a second end <NUM> to the seal housing <NUM>. One exemplary effect of the extension spring is that it does not buckle, and thereby does not need to be held within a bushing to prevent buckling. Furthermore, extension springs do not restrict lateral movement of the rod seal assembly <NUM> and therefore reduce wear on the seal assembly <NUM>. The at least one spring may be a plurality of springs, or may be one single spring, arranged around the bushing <NUM> and the rod seal base <NUM>. The single spring can for example be made from bent sheet metal. <FIG> discloses an embodiment of the rod seal assembly <NUM> provided with a compression spring <NUM>, which comprises two annular wave springs <NUM>. The annular wave springs also has the benefit of not buckle. The wave springs are pressed down towards and shoulder of the bushing <NUM> by a sleeve, which acts between the housing <NUM> and the springs <NUM>.

As the covering <NUM> may be gas permeable, during the working cycle of the engine, there may be gas flow to and from the region sealed by the covering. This is due to the pressure differences throughout the working cycle in combination with the resistance of the gas permeable covering <NUM>. This gas flow may lead to lubricant as aerosols being transferred through the covering <NUM>. This leads to lubricant in the nominally dry region of the cylinder and reduced performance. When using extension springs <NUM> or a wave spring as in <FIG>, the springs <NUM> may be arranged radially outside the rod seal <NUM>, the bushing <NUM>, and the rod seal base <NUM>. The provision of springs outside the rod seal <NUM>, the bushing <NUM> and the rod seal base <NUM> results in a smaller volume inside the region sealed by the covering <NUM>. By reducing the volume sealed by the covering <NUM> this gas flow is reduced, as there is less mass within the volume, and therefore there is less or no transfer of lubricant as aerosols. Hence, even though the rod seal assembly <NUM> embodiments provided with a covering <NUM> and embodiments having an extension springs <NUM> must not be combined the combination thereof gives additional exemplary effects, e.g. less or no transfer of lubricants.

The exemplary embodiment of the rod seal assembly <NUM> of <FIG> (not claimed) is provided with a member <NUM> having lateral compliance greater than its axial compliance may be provided between the rod seal base <NUM> and the seal housing <NUM>. <FIG> discloses different embodiments of the member <NUM>. An embodiment of the member <NUM> as a laminated bearing <NUM> is disclosed in <FIG>. The laminated bearing <NUM> may be provided between the rod seal base <NUM> and the seal housing <NUM>. The laminated bearing <NUM> comprises a plurality of rigid plate layers <NUM> interspaced by compliant layers <NUM>. The compliant layers <NUM> of the laminated bearing <NUM> enable radial and lateral compliance, whilst providing a substantially rigid axial platform. That is, the bearing <NUM> is substantially rigid in the axial direction of the piston rod <NUM> and compliant in the direction perpendicular to the axial direction of the piston rod <NUM>. The laminated bearing <NUM> effectively decouples the lateral forces from the longitudinal axial forces, that is, the forces in line with the axis of the piston rod <NUM>.

The rod seal base <NUM> may be arranged to sit on the laminated bearing <NUM>. The rod seal base <NUM> may be provided with a bearing flange <NUM> which abuts the laminated bearing <NUM> at its upper portion. The laminated bearing <NUM> abuts on the internal base <NUM> of the seal housing <NUM>. The laminated bearing <NUM> may be provided radially outside of the seal <NUM>. In some instances, the seal <NUM> may be excluded, in which case the laminated bearing <NUM> may form the seal at the lower portion of the rod seal base <NUM>.

In one embodiment of the member <NUM>, instead of, or in addition to the laminated bearing <NUM> the rod seal base <NUM> may be provided with a spherical roller bearing (not disclosed), which enable lateral movement of the rod seal base <NUM>. The spherical roller bearing is thereby arranged at the base of the rod seal base <NUM> and contact the internal base <NUM> of the seal housing <NUM>. The spherical roller bearing may be arranged radially outside of the seal <NUM>. The spherical bearings enable guided lateral movement of the rod seal assembly <NUM>.

In one exemplary embodiment of the member <NUM>, disclosed in <FIG>, the member <NUM> comprises a plurality of laterally displaceable, longitudinally pendulous rods <NUM> at which the rod seal base <NUM> is arranged to be supported. In such an arrangement, the seal housing <NUM> is provided with a member <NUM> extending from the internal base <NUM> longitudinally upwards, in the second axial direction AD2 and having a flange <NUM> extending radially inwards towards the piston rod seal <NUM>. The flange <NUM> has recesses <NUM> for receiving each pendulous rod <NUM>. The rod seal base <NUM> is provided with a recess <NUM> for receiving each pendulous rod <NUM>. The rod seal base <NUM> is held longitudinally by the plurality of pendulous rods <NUM>, whilst it can move at least partially laterally. The pendulous rods <NUM> extends between the flange <NUM> of the housing <NUM> and the rod seal base <NUM>.

In one exemplary embodiment of the member <NUM> disclosed in <FIG>, the member <NUM> is a rod bearing <NUM>, which comprises a plurality rods <NUM> arranged between two sheets <NUM>, <NUM>. The plurality of rods <NUM> are axial rigid but provide a lateral flexibility in order to allow the lateral movement of the rod seal base <NUM>. The rod bearing <NUM> is provided to be arranged axial between the rod seal base <NUM> and the internal base <NUM> of the housing.

The different embodiments of the member <NUM> disclosed can be interchanged and combined.

As shown in <FIG>, a labyrinth seal <NUM> may be provided in the bushing <NUM>. The labyrinth seal <NUM> may be provided external to the covering <NUM>, that is, on the opposing side of the covering <NUM> to the rod seal <NUM>, i.e. the high-pressure side HP. The labyrinth seal <NUM> further seals the nominally dry part of the cylinder from the ingress of lubricant. The labyrinth seal <NUM> can comprise one or several recesses in the rod opening of the bushing <NUM>.

<FIG> shows an embodiment of the piston rod seal assembly <NUM> comprising a piston rod <NUM>, an annular rod seal <NUM> arranged around the piston rod <NUM>. The rod seal <NUM> has a lower partial conical portion <NUM>. That is, the lower portion of the rod seal <NUM> has a tapered external surface tapering inwardly toward its center, and therein toward the piston rod <NUM>. The lower conical portion <NUM> is arranged to contact a separate rod seal base <NUM>. The rod seal base <NUM> and the rod seal <NUM> are provided within a seal housing <NUM>. The rod seal base <NUM> seals between the seal housing <NUM> and the rod seal <NUM>. The seal housing <NUM> has a passage <NUM> through which the piston rod <NUM> can be arranged and in which it oscillates. The seal housing <NUM> can furthermore form an enclosure or a partial enclosure for the rod seal assembly <NUM>. The seal housing <NUM> can also be called seal plate or rod seal plate <NUM>.

In <FIG> the exemplary embodiment of the rod seal <NUM> is provided with an internal diameter which tapers outward towards its upper portion <NUM> such that it has an internal diameter Du slightly larger than the external diameter Dp of the piston rod <NUM>, at its upper portion <NUM>. the upper internal diameter Du at the upper portion <NUM> of the rod seal <NUM> is larger than the lower internal diameter Dl of the lower conical portion <NUM> of the rod seal <NUM> and the upper internal diameter Du is thereby larger than the external diameter Dp of the piston rod <NUM>, which is essentially equal to the lower internal diameter Dl. All the embodiments disclosed herein could be provided with such an rod seal <NUM>.

In the exemplary embodiment of the rod seal <NUM> disclosed in <FIG>, Fig. <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, the rod seal base <NUM> forms a conical seat <NUM> for the rod seal <NUM>. The rod seal base <NUM> and the bushing <NUM> forms an overlap <NUM> to align the bushing with the lateral movement of the rod seal base <NUM> and thereby the rod seal <NUM> and the piston rod <NUM>.

To maintain the lower conical portion <NUM> of the rod seal <NUM> within the rod seal base <NUM> a force Fs is applied to the rod seal <NUM> toward the rod seal seat <NUM>. The force Fs is an axial force, that is, it acts in the direction of the longitudinal extension of the rod seal <NUM>. The force Fs may be provided by a plurality of springs <NUM>. The springs <NUM> may apply a force Fs to a bushing <NUM> which is arranged around the rod seal <NUM>.

The bushing <NUM> is arranged radially within the cylindrical wall <NUM> of the rod seal seat <NUM>, or the bushing <NUM> extends in the first axial direction AD1 to be aligned with the rod seal base <NUM> at its base portion <NUM>. The bushing <NUM> has a portion <NUM> for contacting the rod seal <NUM>. The springs <NUM> may be arranged at substantially equal circumferential distances around the bushing <NUM>. The springs <NUM> may be radially outside the bushing <NUM>. That is, the rod seal <NUM> is provided within the bushing <NUM>, the springs <NUM> are provided radially outside the bushing <NUM>. The springs <NUM> may be provided in connection with a flange <NUM> provided at the upper region of the bushing <NUM>. The springs may connect at their first end to the flange <NUM> of the bushing <NUM>, or an element fixed to the bushing <NUM> during operation. The second end of the springs connects to the housing <NUM>.

In the exemplary embodiment according to the invention disclosed in <FIG>, a pressure disc <NUM> is arranged at the housing, axially above the rod seal base <NUM>. The pressure disc <NUM> is provided with a first annular slot, and a second annular slot in its base. The annular slots are provided with a compliant seal rings <NUM>, <NUM>.

The first annular slot has a diameter D3, the diameter defines an area A3.

The rod seal base <NUM> has a recess <NUM> in its base. The recess <NUM> is defined by a pair of walls extending in the first axial direction AD1 from the rod seal base <NUM>, perpendicular to the face of lower surface the rod seal base <NUM>.

The recess <NUM> has a first seal <NUM> provided at the innermost wall of the recess <NUM>. The first seal <NUM> has a diameter D1. The diameter D1 defines and delimits an area A1 which is the area radially within the first seal <NUM>. The area A1 is nominally wet and therefore friction at this area is typically lower than an area which is subject to lubrication during the working cycle.

The recess <NUM> has a second seal <NUM> provided at the outermost wall of the recess <NUM>. That is, radially outside the first seal <NUM>. The second seal <NUM> has a diameter D2.

There is a pressure difference ΔP between the pressure in the crankcase of the hot gas engine, i.e. the low-pressure region LP and the working gas in the cylinder of the hot gas engine, high-pressure region HP. This ΔP applies a normal force to the area A1 at the rod seal <NUM> towards the rod seal seat <NUM>. As the ΔP may be in the order of <NUM> bar, this force may be significant and cause wear at the surface of the rod seal base <NUM> abutting the housing <NUM>.

The diameter of the second seal <NUM> is greater than the diameter of the annular slot providing the upper seal <NUM>.

A pressure relief channel <NUM> is provided in the rod seal base <NUM> from the high-pressure HP region above the pressure disc <NUM>, to the slot <NUM>. The pressure relief channel <NUM> enables the high-pressure working gas to enter the slot <NUM> and thereby equalizing the pressures on both axial sides of the rod seal base <NUM>.

By providing the second seal <NUM> and the upper seal <NUM> with the above relationship the pressure force on the respective axial side of the rod seal base <NUM> becomes the same, whereby the normal force where the rod seal base <NUM> abutting the housing <NUM> is minimized to be essentially equal to the force Fs applied on the rod seal <NUM> by the bushing <NUM>. during the working cycle, it is only the force of the plurality of springs <NUM> which apply a normal force and may cause friction at the rod seal seat <NUM>.

Pressure compensation occurs according to the relationship, where D1, D2, D3 are as defined above, and Dp the diameter of the piston rod.

In the exemplary embodiment disclosed in <FIG> the innermost wall of the recess <NUM> has a reduced height with respect to the outer wall of the recess <NUM>, whereby the contact between the innermost wall of the recess <NUM> and the seal housing <NUM> may be eliminated. The seal housing <NUM> is provided with a channel <NUM> from the lubricated crankcase region of the hot gas engine to the outer wall of the recess <NUM>. This results in the area A2 can be lubricated with lubrication from the piston rod and friction and wear being thus reduced. The force Fs of the springs <NUM> is therefore only acting on the outermost wall of the slot <NUM>, which is lubricated and therefore friction and wear of the components of the rod seal assembly <NUM> is reduced.

As before, the seal housing <NUM> may seal against the wall of the cylinder <NUM>. The radial perimeter <NUM> of the seal housing <NUM> may be provided with an annular slot <NUM>. The annular slot <NUM> may house a seal <NUM>, for example, an O-ring, or similar gasket, which seals the seal housing against the wall of the cylinder.

<FIG> and <FIG> discloses two embodiments of the rod seal assembly <NUM> (not claimed), which is provided with the pressure relief channel <NUM> and the lubrication channel <NUM> as the embodiment disclosed in <FIG>. The main difference between the embodiments in <FIG> and <FIG> and the one in <FIG> is that in the embodiments in <FIG> and <FIG>, the pressure plate <NUM> is replaced with a housing plate <NUM> arranged on the low pressure side LP of the housing <NUM>. The housing plate <NUM> can be screwed or in similar way attached to the housing <NUM>.

The difference between the embodiment in <FIG> and the embodiment in <FIG> is that they are provided with different types of springs <NUM>, which both has been described previously.

Just as for the embodiment disclosed in <FIG>, in the embodiments disclosed in <FIG> and <FIG> a pressure equalizing is achieved through that the pressure relief channel <NUM> connects the space <NUM> between the inner seal ring <NUM> and the outer seal ring <NUM> with the pressure from the high-pressure region HP, and that the upper and lower axial areas of the rod seal base <NUM> exposed to the pressure from the high pressure region HP are essentially equal, such that their resulting pressure force takes out one another. It is also foreseen that the relation between the upper and the lower axial area is such that the resulting pressure force also counteracts the spring force Fs at least partially, in order to reduce the normal force between the rod seal base <NUM> and the housing even more.

The terms axial and longitudinal as used in the present disclosure means in line with the axis of oscillation of the piston rod <NUM>. That is, up and down in the <FIG>. The terms lateral and radial generally mean perpendicular to the axis of oscillation of the piston rod. These definitions are not intended to limit the disclosure but only to clarify the terms in relation to the figures provided and aspects described herein.

Although, the present invention has been described above with reference to specific embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims.

Claim 1:
A rod seal assembly (<NUM>) for a machine comprising a crosshead (<NUM>) and a sealed oscillating piston rod (<NUM>), wherein the rod seal assembly (<NUM>) comprises:
a seal housing (<NUM>), a rod seal (<NUM>), a bushing (<NUM>) and a rod seal base (<NUM>), wherein
the rod seal (<NUM>), the bushing (<NUM>) and the rod seal base (<NUM>) are annular and can be laterally moved in relation to the seal housing (<NUM>)
the housing (<NUM>) axially supports the rod seal base (<NUM>),
the rod seal base (<NUM>) is adapted to be arranged around the piston rod (<NUM>) and is provided with a base portion (<NUM>), wherein the base portion (<NUM>) comprises
a lower axial surface (<NUM>) directed in a first axial direction (AD1),
an upper axial surface (<NUM>) directed in a second axial direction (AD2), wherein
the lower axial surface (<NUM>) abuts the housing (<NUM>) and the upper axial surface (<NUM>) is provided with a rod seal seat (<NUM>),
the rod seal (<NUM>) is adapted to be arranged around the piston rod (<NUM>), and
has a first end portion (<NUM>) and a second end portion (<NUM>), wherein the first end portion (<NUM>) is arranged to connect to the rod seal base (<NUM>) in the first axial direction, and
the bushing (<NUM>) is arranged to abut the rod seal (<NUM>) in the first axial direction,
and the rod seal base (<NUM>) and the bushing are arranged to have an axial overlap (<NUM>),
an inner seal ring (<NUM>) is arranged between lower axial surface (<NUM>) of the base portion (<NUM>) and the seal housing (<NUM>, <NUM>, <NUM>), characterized in that an outer seal ring (<NUM>) is arranged between the lower axial surface (<NUM>) of the base portion (<NUM>) and the seal housing (<NUM>, <NUM>, <NUM>), wherein the outer seal ring (<NUM>) is arranged radially outside the inner seal ring (<NUM>), and
the lower surface (<NUM>) of the base portion is provided with an annular slot (<NUM>) defined by at least one radial inner wall at which the inner seal ring (<NUM>) is arranged and an outer radial wall at which the outer seal ring (<NUM>) is arranged, and the base portion further comprising a pressure relief channel (<NUM>) arranged to connect the lower and the upper axial surfaces (<NUM>, <NUM>) of the base portion.