SE543310C2 - Rod seal assemblies for machines with crossheads and sealed oscillating rods - Google Patents

Abstract

A rod seal assembly (1) for a machine comprising a crosshead and a sealed oscillating piston rod (100), the rod seal assembly (1) comprising: a seal housing (300), an annular rod seal (101) arrangeable around the piston rod (100), the annular rod seal (101) having an internal diameter which tapers outward at an opposite end (102) to an integral or separate annular sealing ring (200) such that it has an internal diameter greater than the external diameter of the piston rod (100), a bushing (400) and at least one spring member (500) arranged to apply at least an axial force to the rod seal (101) such that it is held in place, an annular sealing ring (200) arrangeable around the piston rod (100) and forming a seal at the seal housing (300), the annular sealing ring (200) comprising a cylindrical aligning wall (206) extending longitudinally coaxial with the rod seal (101) and at least partially enclosing and aligning the bushing (400) with respect to the piston rod (100).

Description

ROD SEAL ASSEMBLIES FOR MACHINES WITH CROSSHEADS ANDSEALED OSCILLATING RODS Field of the InventionThe present disclosure relates to rod seal assemblies for hot gas machines. Inparticular it relates to a rod seal assembly comprising an annular sealing ring arrangeable around the piston rod.

Background of the invention In a machine with a sealed oscillating rod, such as a Stirling- engine, -heatpumpor - cryo- machine, there exists a high pressure region within a cylinder separated from arelatively lower pressure region. Clearly, the high pressure region must be sealed fromthe lower pressure region to maintain the pressure difference.

Generally, the piston rod must extend through the seal between the high pressureregion and the low pressure region, resulting in the piston rod seal forrning the primaryseal between the high pressure and low pressure regions.

The piston rod together with the rest of the crank drive is generally alsolubricated. The lubrication may also improve the sealing at the piston rod seal, however,the lubrication must not enter the high pressure region of the cylinder as this would leadto increased wear and reduced efficiency of the engine. The high pressure region of thecylinder is nominally a dry region of the cylinder.

US 4,25l,08l A discloses a piston rod seal comprising a gland with a tubularextension of slightly increasing diameter on the high pressure side. The increasingdiameter leads to a pumping effect at the part having the increased diameter during pistonrod oscillation resulting in minimized oil transport to the high pressure region of thecylinder. A disadvantage in sealing performance of such piston rod seals is, among otherreasons, caused by the fact that piston rods move not only in their axial direction, theyalso move orthogonally/laterally due to some play in the guiding crosshead and pistonguide. Reasons are friction and constrains between the seal and its support with respectto 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.

Summary of the invention Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminateone or more of the above-identified deficiencies in the art and disadvantages singly orin any combination and solves at least the above mentioned problems by providing arod seal assembly for a machine comprising a crosshead and a sealed oscillating pistonrod, the rod seal assembly comprising: a seal housing, an annular rod seal arrangeablearound the piston rod, the annular rod seal having an intemal diameter which tapersoutward at its upper portion such that it has an intemal diameter greater than theextemal diameter of the piston rod, a bushing arranged to apply at least an axial forceto the rod seal such that it is held in place, an annular sealing ring arrangeable aroundthe piston rod and forrning a seal at the seal housing, the annular sealing ringcomprising a cylindrical aligning wall extending longitudinally coaxial with the rodseal and at least partially enclosing and aligning the bushing with respect to the piston rod.

The proposed innovation provides an improved lateral following of the annular seal to the piston rod.

A hot gas engine is also provided.

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

Brief description of the 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 drawings, in which Fig. l is a cross-sectional perspective view of a rod seal assembly according to an aspect.

Fig. 2 is an enlarged partial view of a rod seal assembly according to an aspect.

Fig. 3 is a cross-sectional perspective view of a rod seal assembly according toan aspect.

Fig. 4 is a cross-sectional perspective view of a rod seal assembly according toan aspect.

Fig. 5 is a cross-sectional perspective view of a Stirling engine comprising a rod seal assembly according to an aspect.

Detailed description The present invention relates to a piston rod seal assembly 1 for a machine withcrosshead and a sealed oscillating piston- rod with a rod-seal, such as a hot gas- machine.The rod seal assembly 1 seals a high pressure region in a cylinder from a relatively lowerpressure region. It furtherrnore seals and limits the ingress of lubricant in to the highpressure region of the cylinder. The rod seal assembly 1 disclosed herein results inreduced wear and reduced leakage of the rod seal assembly 1 in cases of lateral movementof the piston rod with reduced wear on the rod seal assembly 1 components. That is, whenthe piston rod moves perpendicular to the axis of extension of the piston rod.

Figure 1 shows a piston rod seal assembly 1 comprising a piston rod 100, acylinder 2, an annular rod seal 101 arranged around the piston rod 100. The rod seal 101having an intemal diameter which tapers outward at its upper portion 102 such that it hasan intemal diameter slightly greater than the extemal diameter of the piston rod 100. Therod seal 101 has a lower partial conical portion 103. That is, the lower portion of the rodseal 101 has a tapered extemal surface tapering inwardly toward its center, and thereintoward the piston rod 100. The lower conical portion 103 is arranged to contact a separateannular sealing ring 200. The rod seal 101 and sealing ring 200 can also be one integralpart. The annular sealing ring 200 and the rod seal 101 are provided within a seal housing300. The annular sealing ring 200 seals at the seal housing 300. The seal housing 300 hasa recess 301 through which the piston rod 100 oscillates. The seal housing 300furtherrnore forms an enclosure for the rod seal assembly 1.

If the annular sealing ring 200 and the rod seal 101 are separate parts, the annularsealing ring 200 may have a partial conical recess 201. The partial conical recess 201 ofthe annular sealing ring 200 forms a conical seat for the rod seal 101. The piston rod 100,the rod seal 101, and the sealing ring 200 may all move laterally with respect to the sealhousing 300. The sealing ring 200 is guided laterally from the piston rod 100. Comparedto existing solutions the provision of the annular sealing ring 200 enables the piston rod100 and rod seal 101 to move laterally and maintain sealing performance. This is becausethe rod seal 101 is not held with respect to the seal housing 300 but is rather free to move, at least slightly, laterally with lateral movements of the piston rod 100.

To maintain the lower conical portion 103 of the rod seal 101 within the sealingring 200 a force is applied to the rod seal 101 toward the sealing ring 200. The force is anaxial force, that is, it acts in the direction of the longitudinal extension of the rod seal 101.The force may be provided by a spring 500. The spring 500 may apply a force to a bushing400 which is arranged around the rod seal 101. The bushing 400 may apply an at leastaxial force to the rod seal 101. The bushing 400 has a portion 402 for contacting the rodseal 101. The bushing 400 may be an annular bushing provided with an external shoulder401 at its lower portion. The external shoulder 401 forrns a seat for the lower portion ofthe spring 500. The spring 500 may be arranged around the bushing 400. The spring 500may be radially outside the bushing 400. That is, the rod seal 101 may be within thebushing 400, the spring 500 may be outside the bushing 400.

Although not shown in the figures, the partial conical recess 201 and the lowerconical portion 103 of the rod seal 101 may instead be flat, laterally extending portionsforrning a pair of mating surfaces. That is, the pair of mating surfaces extend at an angleof 90° to the longitudinal axis of the rod seal 101 and/or piston rod 100. In such anarrangement there is no radial force applied by the sealing ring 200 to the rod seal 101 orvice-versa. The sealing ring 200 and the rod seal 101 apply only an axial force, in linewith the longitudinal axis of the rod seal 101 to each other.

If the rod seal 101 and the annular sealing ring 200 are integral, the conical seat201 of the annular ring 200, and the lower conical portion 103 of the rod seal 101 are notpresent in the assembly. The rod seal 101 comprises a lower portion being the sealingring 200.

The intemal wall of the bushing 400 may be provided with an intemal shoulderportion 402 which may be arranged to interact with a corresponding shoulder portion 104of the lower portion of the rod seal 101. The shoulder portion 104 of the lower portion ofthe rod seal 101 may be a conical portion which tapers radially outward, that is, awayfrom the piston rod 100. If the shoulder portion 104 of the lower portion of the rod seal101 is a conical tapered portion, then the intemal shoulder portion 402 of the bushing 400is a corresponding conical portion, such that the surfaces mate. That is, the intemaltapered portion 402 of the bushing 400 may be arranged to abut with the upper conical portion 104 of the lower portion of the rod seal 101. The corresponding conical portions result in an radial force being applied to the rod seal 101 toward the piston rod 100. Theinternal shoulder portion 402 and the shoulder portion 104 may also be flat, that is, nottapered. The flat surfaces extend laterally outward from the longitudinal axis of the rodseal 101. A flat surface, lacking conical tapers as described above, does not apply anylateral/radial force to the rod seal 101. A force applied by the spring to the bushing 400applies a force to the rod seal 101 to maintain it in position within the sealing ring 200.The lower portion of the bushing 400 may be provided with a lip 403 which extends pastthe upper shoulder portion 104 of the lower portion of the rod seal 101 such that the rodseal is substantially enclosed within the bushing 400. The lip 403 may have an internaldiameter which is greater than the intemal diameter of the upper portion of the bushing400. The cylindrical outer surface 413 of the lip 403 is guided in the cylindrical bore 306of the rod seal housing 300 to limit the buckling of the spring 500 which would tilt thebushing 400 and apply a lateral radial force to the rod seal 101. However, if the rod sealassembly 1 is displaced laterally the compression spring 500 as shown in figures 1 and 2may, in some instances, nevertheless buckle and the lip 403 will not allow lateralmovement of the bushing due to its guiding function. As the bushing 400 cannot movelaterally more than the play between the lip 403 and the rod seal housing allows, thelateral movement of the rod seal is limited A seal 105 may be provided between the upper 104 and lower 103 conicalportions of the rod seal 101. The seal may be for example an O-ring or a similar gasket.The seal may seal against the rod seal 101and the sealing ring 200. The seal at leastpartially forms a pressure tight barrier for the working gas .

The sealing ring 200 is arranged on an intemal base 302 of the seal housing 300.The base of the sealing ring 200 is provided with an annular slot 202. The annular slot202 may be provided with a compliant sealing ring seal 203, for example, an O-ring orsimilar gasket. The annular slot may house the sealing ring seal 203. The sealing ring seal203 may at least partially form a seal separating the nominally dry part of the cylinder,from the nominally lubricated part of the cylinder.

The seal housing 300 may seal against the wall of the cylinder 2. The radialperimeter 303 of the seal housing 300 may be provided with an annular slot 304. The annular slot 304 may house a seal 305, for example, an O-ring, or similar gasket, Whichseals the seal housing against the wall of the cylinder 2.

A covering 600 may be provided above the rod seal 101 to seal against theingress of particles to the lubricant on the piston rod 100. The covering 600 is arrangeddistal the conical seat 201 of the sealing ring 200. That is, the covering 600 is at theopposite end of the rod seal assembly 1 to the sealing ring 200. The covering 600 enclosesa region comprising at least the rod seal 101. The covering 600 may be gas-perrneablesuch that it does not form a gas-tight seal. The covering 600 may be an annular memberwhich is arranged between the bushing 400 and a washer arranged on top of the covering600. The washer is fixed in the seal housing 300 such that the cover 600 is held in placeabove the rod seal 101. The covering may, for example, be an annular covering with acentral aperture for the piston rod 100. The covering may comprise, such as be composedof, a non-woven textile such as a felt. The non-woven textile has the advantage that it isgas-perrneable and absorbs particle matter which may enter the lubricant. The non-woventextile may also partially absorb lubricant. The particle matter present may be metal andplastic wom from the piston rings, piston guides, cylinder liner and other components inthe machine .

To further reduce friction between the seal housing 300 and the sealing ring 200,the slot 202 of the sealing ring 200 may be open at its outer diameter. That is, the slotmay extend to the radial outer wall of the sealing ring 200. The open slot 202 results in asealing ring having an annular recess around its base portion. The annular recess forms aregion of reduced extemal diameter at the base of the sealing ring 200. Minimizingfriction between the sealing ring 200 and the seal housing 300 results in reduced leakageand wear on the rod seal 101, seal housing 300 and piston rod 100. The open annular slot202 results in surface contact between the seal housing 300 and the sealing ring 200 onlyat the lubricated portion of the assembly 1. There is no contact at the nominally dry partof the cylinder which reduces wear.

To further reduce friction between the seal housing 300 and the sealing ring 200,the sealing ring 200 may be coated with a low friction coating such as diamond-likecarbon (DLC) or polytetrafluoroethylene (PTFE) or similar coating. The low-friction coating may be combined with the open slot 202 described above.

To further improve the lateral mobility of the rod seal assembly 1, and thereforereduce friction and wear on the components of the rod seal assembly 1 the sealing ringmay comprise a cylindrical aligning wall as shown in figures 3 and 4.

Figure 3 shows sealing ring 200 having a cylindrical wall 206 extendinglongitudinally from the perimeter of the bottom portion of the sealing ring 200. Thecylindrical wall 206 extends coaxially with the rod seal 101, and piston rod 100. In figure3, the sealing ring 200 comprises a partial conical recess 201. The partial conical recess201 forms a seat for the rod seal 101. As described above, the recess 201 and the rod seal101 may also be flat, such that they form a pair of laterally extending mating surfaces.The cylindrical wall 206 forms an aligning wall partially surrounding the bushing 400,securing that the bushing 400 can follow lateral movements of the rod seal 101 and sealingring 200. The cylindrical aligning wall 206 may surround the bottom portion of thebushing 400. The cylindrical aligning wall 206 may surround the bottom portion of therod seal 101. To keep the rod seal 101 in place, the rod seal 101 is forced towards thesealing ring 200. The bushing 400 is arranged to surround the upper portion of the rodseal 101.

As described above, the sealing ring 200 and the rod seal 101 may be integral.In such an arrangement, the lower portion of the bushing 400 is arranged radially betweenthe upper portion of the rod seal 101 and at least a portion of the cylindrical wall 206.

The base of the sealing ring 200 may be provided with the open annular slot 202as described above. The seal 203, such as an O-ring may be provided at the open annularslot 202. The seal 203 seals the lubricated side of the seal assembly 1 from the non-lubricated, or dry side. As described above, the sealing ring 200 may sit on the intemalbase 302 of the seal housing 300.

A covering 600 may be provided above the rod seal as disclosed above. Thecovering may be gas-perrneable. It may comprise, such as be composed of a non-wovenmaterial which can prevent particles from entering the lubricant. The covering 600 maybe arranged to be held in place by the bushing 400, and/or the rod seal 101. The covering600 may move laterally with the piston rod 100, rod seal 101, bushing 400, and/or sealingring 200.

A plurality of springs 500 may be provided to apply the force to the bushing 400,which applies a force at the rod seal 101 towards the sealing ring 200. The springs 500may be extension springs as shown in figures 3 and 4. The springs may be connected at afirst end 501 to a flange 404 provided on an upper portion of the bushing 400. The flange404 is an annular lateral flange extending around the upper portion of the bushing 400.The springs 500 may be connected at a second end 502 to the seal housing 300. As thesprings are extension springs they do not need to be held within a bushing to preventbuckling. Furtherrnore, the extension springs do not restrict lateral movement of the rodseal assembly 1 and therefore reduce leakage and wear on the seal assembly 1.

As the covering 600 may be gas perrneable, during the working cycle of theengine, there may be gas flow to and from the region sealed by the covering. This is dueto the pressure differences throughout the working cycle in combination with theresistance of the gas perrneable covering 600. This gas flow may lead to lubricant asaerosols being transferred through the covering 600. This leads to lubricant in thenominally dry region of the cylinder and reduced performance.

Compared to figures 1 and 2, as shown in figures 3 and 4, the springs 500 maybe arranged radially outside the rod seal 101, the bushing 400, and the sealing ring 200.The provision of springs outside the rod seal 101, the bushing 400 and the sealing ring200 results in a smaller volume inside the region sealed by the covering 600. By reducingthe volume sealed by the covering 600 this gas flow is reduced, as there is less masswithin the volume, and therefore there is less or no transfer of lubricant as aerosols.

A member 204 having lateral compliance greater than its axial compliance maybe provided between the sealing ring 200 and the seal housing 300. As shown in figure 4,a laminated bearing 204 may be provided between the sealing ring 200 and the sealhousing 300. A laminated bearing 204 comprises a plurality of rigid plate layersinterspaced by compliant layers. The compliant layers of the laminated bearing 204enable radial and lateral compliance, whilst providing a substantially rigid axial platform.That is, the bearing is substantially rigid in the axis of the piston rod 100 and compliantin the direction perpendicular to the axis of the piston rod 100. The laminated bearing 204effectively decouples the lateral forces from the longitudinal axial forces, that is, the forces in line with the axis of the piston rod 100.

The sealing ring 200 may be arranged to sit on the laminated bearing 204. Thesealing ring 200 may be provided with a lower flange 205 which abuts the laminatedbearing 204 at its upper portion. The laminated bearing 204 sits on the internal base 302of the seal housing 300. The laminated bearing 204 may be provided radially outside ofthe seal 203. In some instances, the seal 203 may be excluded, in which case the laminatedbearing 204 may form the seal at the lower portion of the sealing ring 200.

Instead of, or in addition to the laminated bearing 204 the sealing ring 200 maybe provided with a plurality of spherical bearings which enable lateral movement of thesealing ring 200. The plurality of spherical bearings are arranged at the base of the sealingring 200 and contact the intemal base 302 of the seal housing 300. The plurality ofspherical bearings may be arranged radially outside of the seal 203. The sphericalbearings enable guided lateral movement of the rod seal assembly 1.

To further enable guided lateral movement of the sealing ring 200 the sealingring 200 may be arranged to be supported by a plurality of laterally displaceable,longitudinally pendulous rods. In such an arrangement, the seal housing 300 is providedwith a member extending from the intemal base 302 longitudinally upwards, in the axisof piston rod having a flange extending perpendicularly inwards towards the piston rodseal 101. The flange has recesses for receiving each pendulous rod. The sealing ring 200is provided with a recess for receiving each pendulous rod. The sealing ring 200 is heldlongitudinally by the plurality of pendulous rods, whilst it can move at least partiallylaterally. The rod extends between the flange of the housing 400 and the sealing ring 200.

As shown in figure 4, a labyrinth seal 405 may be provided in the bushing 400.The labyrinth seal 405 may be provided extemal to the covering 600, that is, on theopposing side of the covering 600 to the rod seal 101. The labyrinth seal 405 further sealsthe nominally dry part of the cylinder from the ingress of lubricant.

Figure 5 shows a Stirling engine comprising a compression and an expansioncylinder. The cylinders are provided with a rod seal assembly 1 each as shown in figure3.

The terms axial and longitudinal as used in the present disclosure means in linewith the axis of oscillation of the piston rod 100. That is, up and down in the figures 1-4.

The terms lateral and radial generally mean perpendicular to the axis of oscillation of the 11 piston rod. These definitions are not intended to limit the disclosure but only to clarifythe terms in relation to the figures provided and aspects described herein.

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

In the claims, the term “comprises/comprising” does not exclude the presence ofother elements or steps. Additionally, although individual features may be included indifferent claims, these may possibly advantageously be combined, and the inclusion indifferent claims does not imply that a combination of features is not feasible and/oradvantageous. In addition, singular references do not exclude a plurality. The terms “a”,“an”, “f1rst”, “second” etc do not preclude a plurality. Reference signs in the claims areprovided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any Way.

Claims (12)

1. A rod seal assembly (1) for a machine comprising a crosshead and a sealed oscillating piston rod (100), the rod seal assembly (1) comprising:a seal housing (300), an annular rod seal (101) arrangeable around the piston rod (100), and isprovided With an upper portion and a loWer portion (102, 103), and the annularrod seal (101) having an internal diameter Which tapers outWard at its upperportion (102) such that it has an intemal diameter greater than the extemaldiameter of the piston rod (100), and its loWer portion is arranged to contact an annular seal ring (200), a bushing (400) and at least one spring member (500) arranged to apply at leastan axial force to the rod seal (101) via the bushing (400) such that it is held in place, the annular sealing ring (200) arrangeable around the piston rod (100) andforming a seal between the piston rod (100) and the seal housing (300), theannular sealing ring (200) comprising a cylindrical aligning Wall (206)extending longitudinally coaxial With the rod seal (101) and at least partiallyenclo sing and laterally aligning the bushing (400) With respect to the piston rod(100), characterized in thatthe annular sealing ring (200) and the rod seal (101) are separate parts, and the annular sealing ring (200) is provided With a partial conical recess (201) forming a conical seat for the rod seal (101). The rod seal assembly (1) according to claim 1, Wherein the rod seal (101) comprises a shoulder portion (104), and the bushing (400) comprises a corresponding shoulder portion (402) arranged to mate with the shoulder portion (104) ofthe rod seal (101). The rod seal assembly (1) according to claim 2, wherein the shoulder portions(104, 402) are corresponding conical shoulder portions such that a radial force is applied to the rod seal (101) toward the piston rod (100). The rod seal assembly (1) according to any of claims 1 to 2, wherein the sealingring (200) is provided with an open annular slot (202) forrning a region ofreduced external diameter, the open annular slot (202) being provided with a compliant sealing ring seal (203). The rod seal assembly (1) according to any of claims 2 to 4, wherein the rodseal assembly (1) is provided with a gas-perrneable covering (600) arrangeddistal the conical seat (201) of the sealing ring (200), wherein the covering (600)is guided by the bushing (400) such that it follows lateral movements of thepiston rod (100). The rod seal assembly (1) according to any of claims 1 to 5, wherein the at leastone spring member (500) is arranged radially outside of the rod seal (101) andsealing ring (200). The rod seal assembly (1) according to claim 6, wherein the bushing (400) isprovided with a flange (404) and wherein the at least one spring member (500)is an extension spring, and wherein the at least one spring member (500) isarranged radially outside of the bushing (400), between the flange (404) and theseal housing (300). The rod seal assembly (1) according to any of claims 1 to 7, comprising amember having a lateral compliance greater than its axial compliance (204)arranged between the sealing ring (200) and the seal housing (300) for enabling lateral movement of the sealing ring (200). 10. 11. 12. The rod seal assembly (1) according to any of clain1s 1 to 8, Wherein the sealingring (200) is arranged to be supported by a plurality of laterally displaceable, longitudinally pendulous rods. The rod seal assembly according to any of clain1s 1 to 9, Wherein the sealingring (200) is provided With a plurality of spherical bearings, the sphericalbearings being arranged at the base of the sealing ring (200) and contacting theinternal base (302) of the seal housing (300). A n1achine con1prising a crosshead and sealed oscillating piston rod con1prising the rod seal assenibly (1) according to any of clainis 1 to 10. The n1achine according to clain1 11, Wherein the n1achine is a Stirling engine.