Auxiliary bearing system for magnetically supported rotor system

An auxiliary bearing system for a magnetically supported rotor system according to which the auxiliary bearing system includes at least two mounting pad assemblies having compliantly mounted body members.

BACKGROUND

This disclosure relates in general to auxiliary bearing systems, and in particular to an auxiliary bearing system for a magnetically supported rotor system.

In turbomachine systems, if a primary bearing (such as a magnetic bearing) fails, the shaft of the turbomachine will generally fall or drop onto the adjacent mechanical surfaces. This drop often causes substantial damage to the shaft and/or the surrounding components. In turbomachine systems that include an auxiliary bearing, the shaft may drop onto the auxiliary bearing without damaging the shaft or surrounding components.

An auxiliary bearing system is oftentimes subject to extreme accelerations and/or forces during the drop of a shaft operating at high speed, thereby limiting the life of the auxiliary bearing system. To combat these extreme accelerations and/or forces, an auxiliary bearing system may include an inertia ring that is coupled to the shaft. When the primary bearing fails, the inertia ring engages one or more generally stationary surfaces having sacrificial frictional material, thereby regulating the slowdown of the inertia ring. However, potential problems may arise during the operation of a typical inertia ring and its engagement with one or more generally stationary surfaces having sacrificial frictional material. For example, the surfaces having the stationary frictional material may not be able to accommodate the applied load of the shaft, and/or distribute the load among the surfaces. Therefore, what is needed is a system or configuration that overcomes these problems.

SUMMARY

Embodiments of the disclosure may provide an auxiliary bearing system, including at least two mounting pad assemblies may be provided, each mounting pad assembly including a body member compliantly mounted to a casing and permitted to move relative to the casing and the respective body members of other mounting pad assemblies. An inertia ring may be coupled to the shaft, and the inertia ring may engage one or more of the mounting pad assemblies when the shaft is supported by the auxiliary bearing system.

Embodiments of the disclosure may further provide a method of supporting a shaft. The method includes coupling an inertia ring to the shaft, wherein the shaft is at least partially disposed in a casing; compliantly mounting at least two body members to the casing so that each of the body members is permitted to move relative to the casing and the other body members; supporting the shaft with a primary bearing system; and engaging the inertia ring with one or more of the compliantly-mounted body members when the primary bearing system fails.

Embodiments of the disclosure may further provide a rotor system including a shaft and a primary bearing system that supports the shaft during normal operating conditions. An auxiliary bearing system may support the shaft when the primary bearing system fails. The auxiliary bearing system may include an inner ring of a roller element bearing coupled to the shaft, and an outer ring of the roller element bearing disposed radially outward from the inner ring. An inertia ring may be coupled to the outer ring. At least two mounting pad assemblies may be disposed radially outward from the inertia ring, wherein a radial gap is defined between the inertia ring and an inner surface of each of the mounting pad assemblies when the primary bearing system is supporting the shaft. Each of the mounting pad assemblies may be compliantly mounted to a casing.

DETAILED DESCRIPTION

Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope.

In an exemplary embodiment, as illustrated inFIG. 1, a rotor system is generally referred to by the reference numeral10and includes a casing12and a shaft14at least partially disposed therein. The shaft14is normally supported by one or more active magnetic bearing systems (not shown) positioned at one or more axially-spaced locations along the shaft14including, but not limited to, opposing end portions of the shaft14. In several exemplary embodiments, the rotor system10includes, or is part of, a turbomachine such as, for example, a compressor, motor, generator or turbine. The rotor system10further includes an auxiliary bearing system16, which includes a roller element bearing18having an inner bearing ring18athrough which the shaft14extends, and an outer bearing ring18b. The inner bearing ring18ais coupled to the shaft14. An inertia ring20is coupled to the outer bearing ring18b.

The auxiliary bearing system16further includes circumferentially-spaced mounting pad assemblies22,24,26and28. The mounting pad assembly22includes a body member30defining an inner surface30aon which a sacrificial friction material32is disposed. In an exemplary embodiment, the inner surface30ais coated with the friction material32. Circumferentially-spaced openings30band30care formed in each of the opposing axial end portions of the body member30. In an exemplary embodiment, the openings30band30care through openings, resulting in a total of at least two openings formed in the body member30; in an exemplary embodiment, the openings30band30cat each axial end portion are blind openings, resulting in a total of at least four openings formed in the body member30. Axially-extending pins34aand34bextend within the openings30band30c, respectively, and are coupled to the casing12at respective locations outside of the body member30. The openings30band30care oversized with respect to the pins34aand34b, respectively, permitting relative movement between the body member30and the casing12. In an exemplary embodiment, the pins34aand34bare coupled to the casing12by mounting the pins34aand34bin a support structure on either axial side of the auxiliary bearing system16. If the openings30band30care through openings, the pins34aand34bextend through the body member30, resulting in a total of at least two pins. If the openings30band30care blind openings, the pins34aand34bextend into only a portion of the body member30at one axial end portion and pins substantially identical to the pins34aand34bextend into only a portion of the body member30at the other axial end portion.

An outer surface30dof the body member30, which is radially offset from the inner surface30a, is engaged with a portion of a compliant member36, which is engaged with, and extends circumferentially around, the inside surface of the casing12. The compliant member36is configured to provide stiffness, damping and a range of angular compliance. In an exemplary embodiment, the compliant member36is a formed metal strip or sheet. In an exemplary embodiment, the compliant member36is or includes a bump foil, a Borelli ribbon, a tolerance ring segment, knitted metal mesh, an elastomeric support arrangement, parallel flexures, curved beams, and/or any combination thereof. In several exemplary embodiments, the Borelli ribbon may include a compliant ribbon-shaped structure, and the bump foil may include a foil having a series of uniform, axially-extending corrugations or bumps. In an exemplary embodiment, the compliant member36includes one or more embodiments disclosed in U.S. Pat. No. 4,223,958 to Gray, the entire disclosure of which is incorporated herein by reference to the extent the incorporated disclosure is not inconsistent with the present disclosure. In an exemplary embodiment, instead of extending circumferentially around the inside surface of the casing12, the compliant member36is divided into a plurality of arcuate segments, each of which is engaged with the inside surface of the casing12and positioned between a respective body member of one of the mounting pad assemblies22,24,26and28. The engagement of the outer surface30dwith the compliant member36provides a compliant mount for the body member30.

As shown inFIG. 1, the body member30is biased away from the inside surface of the casing12by the compliant member36and held in place by the pins34aand34b, thereby preloading the body member30against the compliant member36and holding the body member30(and thus the friction material32) radially away from the inertia ring20under conditions to be described below. The openings30band30care oversized to allow angular compliance, to prevent the body member30from rotating, and to permit movement of the body member30relative to the casing12and the other mounting pad assemblies24,26and28.

Each of the mounting pad assemblies24,26and28is substantially identical to the mounting pad assembly22, and therefore the mounting pad assemblies24,26and28will not be described in further detail. The components of each of the mounting pad assemblies24,26and28are given the same reference numerals as the corresponding components of the mounting pad assembly22.

In several exemplary embodiments, in addition to the mounting pad assemblies22,24,26and28, the auxiliary bearing system16may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly22. In several exemplary embodiments, one or more of the mounting pad assemblies22,24,26and28may be omitted from the auxiliary bearing system16. In an exemplary embodiment, the auxiliary bearing system16may include only two of the mounting pad assemblies22,24,26and28.

During normal operation of the rotor system10, that is, when the active magnetic bearings systems are supporting the shaft14, the shaft14rotates and a radial clearance or gap38is defined between the inertia ring20and the friction material32. The shaft14is levitated, relative to the casing12and the mounting pad assemblies22,24,26and28, by the one or more active magnetic bearing systems, and the shaft14, the roller element bearing18including the rings18aand18b, and the inertia ring20all rotate relative to the casing12and the mounting pad assemblies22,24,26and28, all of which are generally stationary. The auxiliary bearing system16does not support the shaft14during the normal operation of the rotor system10. However, since the inner ring18aof the roller element bearing18is coupled to the shaft14, the roller element bearing18and the inertia ring20rotate or spin in place along with the shaft14during the normal operation of the rotor system10.

When one or more of the magnetic bearing systems—which support the shaft14during normal operation of the rotor system10—fail, the shaft14delevitates so that the inertia ring20engages or drops onto one or both of the mounting pad assemblies22and28, at which point the auxiliary bearing system16begins to at least partially support the spinning shaft14, with the roller element bearing18being subjected to, and accommodating, at least a radial load. The inertia ring20increases the mass of the outer bearing ring18band therefore slows the rate of deceleration of the outer bearing ring18bduring the drop event. Upon engagement with the mounting pad assemblies22and/or28, the inertia ring20contacts the friction material32of the mounting pad assembly22and/or the friction material32of the assembly28, which friction material(s) regulate the slowdown of the inertia ring20and prevent damage to the engaging surfaces of the inertia ring20and the respective body members30. Due to the compliant mounting of the respective body members30, the mounting pad assemblies22and/or28absorb impact loads due to the drop of the shaft14and provide prescribed amounts of stiffness and damping to the auxiliary bearing system16, thereby facilitating vibration control of the shaft14when traversing critical speeds during coastdown. The controlled deceleration of the components of the auxiliary bearing system16, including the roller element bearing18and the inertia ring20, allow the auxiliary bearing system16to tolerate an increased number of drop events of the shaft14. Moreover, there are no unlubricated moving contacts once the transient motion associated with a drop event has ceased. In an exemplary embodiment, if the shaft14delevitates and engages two or more of the mounting pad assemblies22,24,26and28, the shaft14is supported at two or more discrete points, thereby minimizing any tendency for the shaft14to whirl.

During the engagement of the inertia ring20with the mounting pad assembly22, at least the compliant mount provided by the engagement of the body member30with the compliant member36, and/or the oversized openings30band30c, allow the body member30to move and/or pivot to best accommodate the applied load. For example, the body member30or a portion thereof may move by pivoting about, for example, an axis that is generally parallel to the shaft, and/or translating radially, axially, circumferentially, and/or any combination thereof. Similarly, in addition to the engagement of the inertia ring20with the mounting pad assembly22, the corresponding compliant mount(s) provided by one or more of the mounting pad assemblies24,26and28, and the corresponding pairs of oversized openings30band30c, allow the corresponding body members30to move by pivoting and/or translating to best accommodate the applied load, and to distribute the load among the mounting pad assembly22and the one or more of the mounting pad assemblies24,26and28. As a result, two or more of the mounting pad assemblies22,24,26and28cradle the mass of the inertia ring22and share the load.

Since the respective body members30of the mounting pad assemblies22,24,26and28are compliantly mounted to the casing12and the body members30have some degree of movement to better support the load(s) on them, the mounting pad assemblies22,24,26and28support the shaft14in a stable position if, as a result of the failure of one or more of the magnetic bearing systems and the delevitation of the shaft14, one or more loads are in line with one or more of the respective body members30and/or if one or more loads are between adjacent ones of the respective body members30.

In an exemplary embodiment, as illustrated inFIG. 2with continuing reference toFIG. 1, a rotor system is generally referred to by the reference numeral40and includes an auxiliary bearing system42, which contains several parts of the auxiliary bearing system16, which are given the same reference numerals. The auxiliary bearing system42includes circumferentially-spaced mounting pad assemblies44,46,48and50. The mounting pad assembly44is substantially similar to the mounting pad assembly22, except that the compliant member36, the openings30band30c, and the pins34aand34b, are omitted in favor of T-shaped slots30eand30fand curved beam supports52aand52b, which are coupled to the inside wall of the casing12. The curved beam supports52aand52binclude bases52aaand52ba,from which T-shaped protrusions52aband52bb,respectively, extend radially inward. The slots30eand30fare formed in the surface30dof the body member30, and the T-shaped protrusions52aband52bbextend within the slots30eand30f, respectively, thereby engaging the body member30and thus compliantly mounting the body member30. A gap54is defined between the body member30and bases52aaand52ba.

Each of the mounting pad assemblies46,48and50is substantially identical to the mounting pad assembly44and therefore the mounting pad assemblies46,48and50will not be described in further detail. The components of each of the mounting pad assemblies46,48and50are given the same reference numerals as the corresponding components of the mounting pad assembly44.

In several exemplary embodiments, in addition to the mounting pad assemblies44,46,48and50, the auxiliary bearing system42may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly44. In several exemplary embodiments, one or more of the mounting pad assemblies44,46,48and50may be omitted from the auxiliary bearing system42. In an exemplary embodiment, the auxiliary bearing system42may include only two of the mounting pad assemblies44,46,48and50.

The operation of the rotor system40, including the operation of its auxiliary bearing system42, is similar to the above-described operation of the rotor system10, including the above-described operation of its auxiliary bearing system16, and therefore the operation of the rotor system40and the auxiliary bearing system42will not be described in detail. At least the compliant mounts provided by the respective engagements between the body members30and the corresponding curved beams52aand52b, and/or the respective gaps54, allow the body members30of the auxiliary bearing system42to move and/or pivot to best accommodate and/or distribute the applied load when one or more of the magnetic bearing systems normally supporting the rotating shaft14fail.

In an exemplary embodiment, as illustrated inFIGS. 3 and 3Awith continuing reference toFIGS. 1 and 2, a rotor system is generally referred to by the reference numeral56and includes the casing12, the shaft14and an auxiliary bearing system58, which, in turn, includes the roller element bearing18, the inertia ring20, and circumferentially spaced mounting pad assemblies60,62,64and65. The mounting pad assembly60includes an arcuate body member66defining an inner surface66aon which the friction material32is disposed. In an exemplary embodiment, the inner surface66ais coated with the friction material32. Circumferentially-spaced openings66band66care formed in each of the opposing axial end portions of the body member66. Axially-extending pins68aand68bextend through the openings66band66c, respectively, and are coupled to the casing12at respective locations outside of the body member66. In an exemplary embodiment, the pins68aand68bare coupled to the casing12by mounting the pins68aand68bin a support structure on either axial side of the auxiliary bearing system58. The openings66band66care oversized with respect to the pins68aand68b, respectively, permitting relative movement between the body member66and, for example, the casing12and the mounting assemblies62,64and65.

The body member66further defines an outer surface66d, which is radially offset from the inner surface66a, and which includes a radius of curvature in the circumferential direction (as viewed inFIG. 3) that is less than the radius of curvature of the surface66a. The outer surface66dalso includes a radius of curvature in the axial direction (as viewed in FIG.3A)—this may be referred to as a “double-tilt” configuration. The outer surface66dof the body member66is engaged with a portion of a circumferentially-extending casing or housing70, which, in turn, is engaged with the compliant member36and thus is compliantly mounted. Due to the curvature of the outer surface66d, the body member66is able to rock on the inside surface of the housing70. In an exemplary embodiment, the outer surface66dincludes a radius of curvature in the circumferential direction (as viewed inFIG. 3), but the outer surface66ddoes not include a radius of curvature in the axial direction. This may be referred to as a “single-tilt” configuration. Axially-extending shoulders66daand66dbare formed on opposing circumferential end portions of the body member66. Hold-down springs71aaand71abare disposed on the shoulders66daand66db,respectively. In an exemplary embodiment, each of the hold-down springs71aaand71abincludes a wave spring. Generally L-shaped protrusions71baand71bbextend from the inside surface of the housing70, and the smaller legs of the protrusions71baand71bbextend over, and engage, the hold-down springs71aaand71ab,respectively, thereby providing a radial retention mechanism or hold-down arrangement.

Each of the mounting pad assemblies62,64and65is substantially identical to the mounting pad assembly60and therefore the mounting pad assemblies62,64and65will not be described in further detail. The components of each of the mounting pad assemblies62,64and65are given the same reference numerals as the corresponding components of the mounting pad assembly60. The engagements between the L-shaped protrusions71baand71bband the hold-down springs71aaand71ab,respectively, keep the respective body members66of the mounting pad assemblies62and64from falling down, as viewed inFIG. 3.

In several exemplary embodiments, in addition to the mounting pad assemblies60,62,64and65, the auxiliary bearing system58may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly60. In several exemplary embodiments, one or more of the mounting pad assemblies60,62,64and65may be omitted from the auxiliary bearing system58. In an exemplary embodiment, the auxiliary bearing system58may include only two of the mounting pad assemblies60,62,64and65.

The operation of the rotor system56, including the operation of its auxiliary bearing system58, is similar to the above-described operation of the rotor system10, including the above-described operation of its auxiliary bearing system16, and therefore the operation of the rotor system56and the auxiliary bearing system58will not be described in detail. At least the compliant mount provided by the engagement between the housing70and the compliant member36, and/or the rocking ability of the respective body members66, allow the body members66of the auxiliary bearing system58to move and/or pivot to best accommodate and/or distribute the applied load when one or more of the magnetic bearing systems normally supporting the rotating shaft14fail.

In an exemplary embodiment, as illustrated inFIG. 4with continuing reference toFIGS. 1-3, a rotor system is generally referred to by the reference numeral72and includes the casing12, the shaft14and an auxiliary bearing system74, which, in turn, includes the roller element bearing18, the inertia ring20, and circumferentially spaced mounting pad assemblies76,78,80and82. The mounting pad assembly76includes an arcuate body member84defining an inner surface84aon which the friction material32is disposed. In an exemplary embodiment, the inner surface84ais coated with the friction material32. Axially-extending shoulders84band84care formed on opposing circumferential end portions of the body member84. The body member84is mounted on compliant inserts86aand86b, which extend between the casing12and the body member84. The compliant inserts86aand86bhave both stiffness and damping. In an exemplary embodiment, the compliant inserts86aand86bare knitted mesh metal inserts (as shown inFIG. 4), elastomer “button” inserts, shear mounts, and/or any combination thereof. In an exemplary embodiment, if the inserts86aand86bare knitted mesh metal inserts, the inserts86aand86bmay be fabricated from knitted mesh material available from Metal Textiles Corporation or Stop-Choc. Generally L-shaped protrusions88aand88bextend from the inside surface of the casing12and the smaller legs of the protrusions88aand88bextend over the shoulders84band84c, respectively, of the body member84.

As shown inFIG. 4, the body member84is biased away from the inside surface of the casing12by the compliant inserts86aand86band held in place by the L-shaped protrusions88aand88b, thereby preloading the body member84against the compliant inserts86aand86band holding the body member84(and thus the friction material32) radially away from the inertia ring20. A gap90is defined between the body member84and the inside surface of the casing12.

Each of the mounting pad assemblies78,80and82is substantially identical to the mounting pad assembly76and therefore the mounting pad assemblies78,80and82will not be described in further detail. The components of each of the mounting pad assemblies78,80and82are given the same reference numerals as the corresponding components of the mounting pad assembly76.

In several exemplary embodiments, in addition to the mounting pad assemblies76,78,80and82, the auxiliary bearing system74may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly76. In several exemplary embodiments, one or more of the mounting pad assemblies76,78,80and82may be omitted from the auxiliary bearing system74. In an exemplary embodiment, the auxiliary bearing system74may include only two of the mounting pad assemblies76,78,80and82.

The operation of the rotor system72, including the operation of its auxiliary bearing system74, is similar to the above-described operation of the rotor system10, including the above-described operation of its auxiliary bearing system16, and therefore the operation of the rotor system72and the auxiliary bearing system74will not be described in detail. At least the compliant mounts provided by the respective engagements between the body members84and the corresponding inserts86aand86b, and/or the respective gaps90, allow the body members84of the auxiliary bearing system74to move and/or pivot to best accommodate and/or distribute the applied load when one or more of the magnetic bearing systems normally supporting the rotating shaft14fail.

In an exemplary embodiment, as illustrated inFIGS. 5 and 5Awith continuing reference toFIGS. 1-4, a rotor system is generally referred to by the reference numeral92and includes an auxiliary bearing system94, which contains several parts of the auxiliary bearing system58, which are given the same reference numerals. The auxiliary bearing system94includes circumferentially-spaced mounting pad assemblies96,98,100and102. The mounting pad assembly96is substantially similar to the mounting pad assembly60, except that the openings66band66c, and the pins68aand68b, are omitted in favor of an alternative retainment system104, which retains the body member66.

The retainment system104includes a post106having a threaded end portion106aand a head end portion106bopposed thereto, the head end portion106bdefining a circumferentially-extending crowned surface106ba.A blind opening66eis formed in the surface66dof the body member66, and the head end portion106bextends within the opening66e. A flat nut108is threadably engaged with an internal threaded connection formed in the inside surface of the body member66defined by the opening66e. A spring110is disposed within the opening66eso that the spring110extends between the head end portion106band the flat nut108, and so that the post106extends through the spring110. The post106is fastened to the outer surface of the housing70via a nut112. The radial preload force on the body member66can be adjusted by changing the length of the post106(and therefore the amount of compression) and/or changing the spring110to include either a heavier or lighter spring or, in several exemplary embodiments, changing the spring110to be in the form of another device that provides a spring force such as, for example, a Belleville washer arrangement. The pivot point or location, that is, the location on the surface66dthat serves as the center of contact with the housing70for the unloaded mounting pad assembly96, is illustrated inFIG. 3to be at the circumferential center of the body member66, circumferentially equidistant from the ends of the body member60. However, in several exemplary embodiments, the pivot point may be located at a different circumferential point along the body member66, either with or against the rotation of the shaft14from the circumferential center of the body member66, as viewed inFIG. 3.

Each of the mounting pad assemblies98,100and102is substantially identical to the mounting pad assembly96and therefore the mounting pad assemblies98,100and102will not be described in further detail. The components of each of the mounting pad assemblies98,100and102are given the same reference numerals as the corresponding components of the mounting pad assembly96.

In several exemplary embodiments, in addition to the mounting pad assemblies96,98,100and102, the auxiliary bearing system94may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly96. In several exemplary embodiments, one or more of the mounting pad assemblies96,98,100and102may be omitted from the auxiliary bearing system94. In an exemplary embodiment, the auxiliary bearing system94may include only two of the mounting pad assemblies96,98,100and102.

The operation of the rotor system92, including the operation of its auxiliary bearing system94, is similar to the above-described operation of the rotor system10, including the above-described operation of its auxiliary bearing system16, and therefore the operation of the rotor system92and the auxiliary bearing system94will not be described in detail. At least the compliant mount provided by the engagement between the housing70and the compliant member36, and/or the rocking ability of the respective body members66, allow the body members66of the auxiliary bearing system94to move and/or pivot to best accommodate and/or distribute the applied load when one or more of the magnetic bearing systems normally supporting the rotating shaft14fail. During operation, each of the crowned surfaces106baof the head end portion106bprevents the respective body member66from being dragged by the inertia ring20during a drop or touchdown event.

In an exemplary embodiment, as illustrated inFIG. 6with continuing reference toFIGS. 1-5A, a rotor system is generally referred to by the reference numeral114and includes the casing12, the shaft14and an auxiliary bearing system116, which, in turn, includes the roller element bearing18, the inertia ring20, and circumferentially spaced mounting pad assemblies118,120,122and124. The mounting pad assembly118includes an arcuate body member126defining an inner surface126aon which the friction material32is disposed. In an exemplary embodiment, the inner surface126ais coated with the friction material32. A socket126bis formed in an outer surface126cof the body member126, the surface126cbeing radially offset from the inner surface126a. A protrusion128extends radially inward from the inside surface of the casing12. A through opening130is formed through the casing12and the protrusion128. A post132including a ball end portion132aand an opposing flat head end portion132bextends within the opening130so that the ball end portion132ais engaged with the socket126b. Due to this ball-and-socket engagement, the body member126is permitted to rock and/or rotate, relative to at least the casing12. A plug134is threadably engaged with an internal threaded connection formed in the inside surface of the casing12defined by the opening130. A spring136is disposed within the opening130and extends between the flat head end portion132bof the post132and the plug134. As a result of the engagement between the body member126and the post132and the engagement between the post132and the spring136, the body member126is compliantly mounted. The plug134provides compression adjustment. A gap138is defined between the outer surface126cof the body member126and the protrusion128. Axially-extending shoulders126daand126dbare formed on opposing circumferential end portions of the body member126. Hold-down springs139aaand139abare disposed on the shoulders126daand126db,respectively; in an exemplary embodiment, each of the hold-down springs139aaand139abincludes a wave spring. Generally L-shaped protrusions139baand139bbextend from the inside surface of the casing12and the smaller legs of the protrusions139baand139bbextend over, and engage, the hold-down springs139aaand139ab,respectively, thereby providing a radial retention mechanism or hold-down arrangement.

Each of the mounting pad assemblies120,122and124is substantially identical to the mounting pad assembly118and therefore the mounting pad assemblies120,122and124will not be described in further detail. The components of each of the mounting pad assemblies120,122and124are given the same reference numerals as the corresponding components of the mounting pad assembly118. The engagements between the L-shaped protrusions139baand139bband the hold-down springs139aaand139ab,respectively, keep the respective body members126of the mounting pad assemblies120and124from falling down onto the inertia ring20, as viewed inFIG. 6.

In several exemplary embodiments, in addition to the mounting pad assemblies118,120,122and124, the auxiliary bearing system116may include one or more other mounting pad assemblies substantially identical to the mounting pad assembly118. In several exemplary embodiments, one or more of the mounting pad assemblies118,120,122and124may be omitted from the auxiliary bearing system116. In an exemplary embodiment, the auxiliary bearing system116may include only two of the mounting pad assemblies118,120,122and124.

The operation of the rotor system114, including the operation of its auxiliary bearing system116, is similar to the above-described operation of the rotor system10, including the above-described operation of its auxiliary bearing system16, and therefore the operation of the systems114and116will not be described in detail. At least the respective compliant mountings of the body members126, the respective engagements of the ball end portions132awith the corresponding sockets126b, and/or the respective gaps138, allow the body members126of the auxiliary bearing system116to move and/or pivot to best accommodate and/or distribute the applied load when one or more of the magnetic bearing systems normally supporting the rotating shaft14fail.

In an exemplary embodiment, as illustrated inFIG. 7with continuing reference toFIGS. 1-6, a rotor system is generally referred to by the reference numeral140and includes a shaft142and a magnetic bearing system144, which is one of a plurality of magnetic bearing systems that normally support the shaft142and are positioned at axially-spaced locations along the shaft142. The rotor system140further includes an auxiliary bearing system146, which is one of a plurality of auxiliary bearing systems that are positioned at axially-spaced locations along the shaft142. The auxiliary bearing system146supports the shaft142when the magnetic bearing system144fails. In several exemplary embodiments, the auxiliary bearing system146is the auxiliary bearing system16,42,58,74,94or116, as described above, or an auxiliary bearing system148, as described below and illustrated inFIGS. 8-12. In several exemplary embodiments, the rotor system140includes, or is part of, a turbomachine such as, for example, a compressor, turbine, motor or generator.

In an exemplary embodiment, as illustrated inFIGS. 8-12, a rotor system is generally referred to by the reference numeral150and includes a casing152and a shaft154at least partially disposed therein, the shaft154being normally supported by one or more active magnetic bearing systems positioned at one or more axially-spaced locations along the shaft154including, but not limited to, opposing end portions of the shaft154. In several exemplary embodiments, the rotor system150includes, or is part of, a turbomachine such as, for example, a compressor, motor, generator or turbine. The rotor system150further includes the auxiliary bearing system148, which includes a roller element bearing156having an inner bearing ring156athrough which the shaft154extends, and an outer bearing ring156b. The inner bearing ring156ais coupled to the shaft154. An inertia ring158is coupled to the outer bearing ring156b.

The auxiliary bearing system148further includes a plurality of circumferentially-spaced mounting pad assemblies160, which are spaced about the inertia ring158. Each of the mounting pad assemblies160includes an annular body member162that is, in several exemplary embodiments, nominally concentric with the shaft154. Each of the body members162includes a U-shaped channel162a, which defines inner surfaces162b,162cand162d. Each of the body members162defines an outer surface162e, which is radially offset from the inner surface162c. A plurality of blind counterbores163are formed in the outer surface162eof each of the body members162, each of the counterbores163including an enlarged diameter portion163aand a reduced diameter portion163bhaving an internal threaded connection163ba.

A pad of sacrificial friction material164is disposed on, and coupled to, the inner surfaces162b,162cand162dof each of the body members162. In an exemplary embodiment, the inner surfaces162b,162cand162dare coated with the friction material164. In an exemplary embodiment, the pad of friction material164is coupled to the inside surfaces162b,162cand162dof each of the body members162via one or more adhesives, rivets, screws, other fastening systems, and/or any combination thereof. In an exemplary embodiment, the friction material164is made from a material having capabilities that are similar to the capabilities of clutch facing material. In an exemplary embodiment, the friction material164is a Kevlar fiber matrix. Under conditions to be described below, the friction material164is adapted to engage the inertia ring158, the outer surface of which, in several exemplary embodiments, is made of a material that provides an appropriate abrasion resistant tribologic pair with the friction material164such as, for example, cast iron or steel.

A channel166is formed in the outer surface162eof each of the body members162, and extends generally along the perimeter of the body member162. A sealing element such as an o-ring168is disposed in each of the channels166. A casing or housing170is coupled to the inside surface of the casing152, and is also coupled to the respective body members162of the mounting pad assemblies160. For each of the body members162, a plurality of counterbores172are formed through the housing170, each of the counterbores172having an enlarged diameter portion172aand a reduced diameter portion172b, and being aligned with a respective one of the counterbores163formed in the body member162.

Each of the body members162is compliantly mounted to the housing170. More particularly, a plurality of fasteners174extend through the counterbores172and into the counterbores163, respectively. Each of the fasteners174includes a head174aand an enlarged diameter portion174bextending therefrom, and a reduced diameter portion174cextending from the enlarged diameter portion174b, the reduced diameter portion174cincluding an external threaded connection174ca.For each of the fasteners174, the head174aengages an internal shoulder of the housing170defined by the enlarged diameter portion172aof a respective one of the counterbores172, the enlarged diameter portion174bextends through the reduced diameter portion172b, the end of the enlarged diameter portion174bengages an internal shoulder of the body member162defined by the enlarged diameter portion163aof a respective one of the counterbores163, the reduced diameter portion174cextends into the reduced diameter portion163b, and the external threaded connection174ca engages the internal threaded connection163ba,thereby coupling the body member162to the housing170. As a result of the respective extensions of the fasteners174through the counterbores172and into the counterbores163and the resulting coupling of the body member162to the housing170, the o-ring168is compressed and thus sealingly engages the inside surface of the housing170and the outside surface162eof the body member162. An o-ring176extends in an annular channel formed in the outside surface of the enlarged diameter portion174bof each of the fasteners174, the o-ring sealingly engaging the inside wall of the housing170defined by the reduced diameter portion172bof the respective counterbore172. In an exemplary embodiment, an annular element178extends about the enlarged diameter portion174bof each of the fasteners174, and is positioned between the inside surface of the housing170and the outer surface162eof the body member162. In an exemplary embodiment, the annular elements178are compressed between the body member162and the housing170. The coupling of the housing170to the body member162via the fasteners174, the compression of the o-ring168, the positioning of the annular elements178between the housing170and the body member162, and/or any combination thereof, provides a compliant mount for the body member162. In several exemplary embodiments, instead of, or in addition to employing the fasteners174and/or the annular elements178, each of the body members162may be compliantly mounted to the housing170with one or more of the compliant mounts described above and illustrated inFIGS. 1-6.

As a result of the above-described coupling of each of the body members162to the housing170, a cavity180is defined radially between the surface162eof each of the body members162and the inside surface of the housing170, and is further defined by the respective o-ring168. An axisymmetric annulus182is formed in the housing170. Each of the cavities180is fluidically coupled to the annulus182via a porous fluid communication path184. In an exemplary embodiment, each of the porous fluid communication paths184is a series of small through-holes, a matrix of porous media, and/or any combination thereof. The cavities180are filled with a fluid such as, for example, lubricating oil, which is also disposed in the annulus182, which serves as a common fluid reservoir for all of the cavities180in the auxiliary bearing system148. A pressure compensation device186is fluidically and/or otherwise operably coupled to the annulus182, and is capable of adjusting and maintaining the fluid content and pressure within the annulus182, the fluid communication paths184, and the cavities180. In an exemplary embodiment, the pressure compensation device186includes one or more bellows, piston/spring systems, remote sources of pressurized fluid, and/or any combination thereof.

In operation, in an exemplary embodiment with continuing reference toFIGS. 8-12, the shaft154rotates in place during the operation of the rotor system150, and is normally supported by one or more magnetic bearing systems positioned at one or more axially-spaced locations along the shaft154including, but not limited, opposing end portions of the shaft154. During the rotation of the shaft154and its normal support by the active magnetic bearing systems, a radial clearance or gap is defined between the inertia ring158and the pads of the friction material164. The shaft154is levitated, relative to the casing152, the housing170and the mounting pad assemblies160, by the one or more active magnetic bearing systems, and the shaft154, the roller element bearing156including the rings156aand156b, and the inertia ring158all rotate relative to the casing152, the housing170and the mounting pad assemblies160, all of which are generally stationary. The auxiliary bearing system148does not support the shaft154during the normal operation of the rotor system150, that is, when the active magnetic bearing systems are supporting the shaft154. However, since the inner ring156aof the roller element bearing156is coupled to the shaft154, the roller element bearing156and the inertia ring158rotate or spin in place along with the shaft154during the normal operation of the rotor system150.

When one or more of the magnetic bearing systems—which normally support the shaft154—fail, the shaft154delevitates so that the inertia ring158engages or drops onto one or more of the mounting pad assemblies160, at which point the auxiliary bearing system148begins to at least partially support the spinning shaft154, with the roller element bearing156being subjected to, and accommodating, at least a radial load. The mass of the inertia ring158is added to the outer bearing ring156band therefore slows the rate of deceleration of the outer bearing ring156bduring the drop event. Upon engagement with one or more of the mounting pad assemblies160, the inertia ring158contacts the respective pads of the friction material164, which regulate the slowdown of the inertia ring158and prevent damage to the engaging surfaces of the inertia ring158and the respective body members162. Due to the compliant mounting of the respective body members162, the mounting pad assemblies160absorb impact loads due to the drop of the shaft154and provide prescribed amounts of stiffness and damping to the auxiliary bearing system148, thereby facilitating vibration control of the shaft154when traversing critical speeds during coastdown. The controlled deceleration of the components of the auxiliary bearing system148, including the roller element bearing156and the inertia ring158, allow the auxiliary bearing system148to tolerate an increased number of drop events of the shaft154. Moreover, there are no unlubricated moving contacts once the transient motion associated with a drop event has ceased. In an exemplary embodiment, if the shaft154delevitates and engages two or more of the mounting pad assemblies160, the shaft154is supported at two or more discrete points, thereby minimizing any tendency for the shaft154to whirl.

During the engagement of the inertia ring158with at least one of the mounting pad assemblies160, the above-described compliant mounting of the respective body member162to the housing170allows the body member162to move and/or pivot to best accommodate the applied load. For example, the body member162or a portion thereof may move by pivoting about, for example, an axis that is generally parallel to the shaft154, and/or translating radially, axially, circumferentially, and/or any combination thereof. Similarly, during the engagement of the inertia ring158with two or more of the mounting pad assemblies160, the above-described compliant mounting of the respective body members162to the housing170allow the respective body members162to move by pivoting and/or translating to best accommodate the applied load, and to distribute the load among the mounting pad assemblies160. As a result, two or more of the mounting pad assemblies160cradle the mass of the inertia ring158and share the load.

Since the respective body members162of the mounting pad assemblies160are compliantly mounted to the housing170and the body members162have some degree of movement to better support the load(s) on them, the mounting pad assemblies160support the shaft154in a stable position if, as a result of the failure of one or more of the magnetic bearing systems and the delevitation of the shaft154, one or more loads are in line with one or more of the respective body members162and/or if one or more loads are between adjacent ones of the respective body members162.

Before, during or after the engagement of the inertia ring158with at least one of the mounting pad assemblies160, and when the respective body member162moves at least radially outwardly towards the housing170in response to the engagement and/or subsequent disengagement, at least a portion of the fluid in the respective cavity180is driven out of the cavity180and flows into the annulus182via the respective porous communication path184. More particularly, the pad of friction material164, the body member162and the corresponding fasteners174move at least radially outwardly towards the housing170, reducing the radial dimension of the cavity180, that is, the radial spacing between the surface162eof the body member162and the inside surface of the housing170, thereby driving at least a portion of the fluid in the cavity180through the porous communication path184and into the annulus182. The porous communication path184provides linear, or nearly linear, damping when the fluid is driven out of or into the cavity180.

Before, during or after the engagement of the inertia ring158with at least one of the mounting pad assemblies160, and when the respective body member162moves at least radially inwardly away from the housing170in response to the engagement and/or subsequent disengagement, at least a portion of the fluid in the annulus182is drawn into the cavity180via the respective porous communication path184. More particularly, the pad of friction material164, the body member162and the corresponding fasteners174move at least radially inwardly away from the housing170, increasing the radial dimension of the cavity180, that is, the radial spacing between the surface162eof the body member162and the inside surface of the housing170, thereby drawing at least a portion of the fluid in the annulus182through the porous communication path184and into the cavity180. The porous communication path184provides linear, or nearly linear, damping when the fluid is drawn into the cavity180.

The respective porous fluid communication paths184of the mounting pad assemblies160provide linear, or nearly linear, damping when fluid is driven out of, or drawn into, the respective cavities180via the porous fluid communication paths184over a large range of fluid flow, with the fluid flow being driven by the respective radial movements of the body members162of the mounting pad assemblies160, relative to the housing170, as indicated by an arrow188inFIG. 12, and with the pressure compensation device186maintaining the fluid content and pressure within the annulus182, the fluid communication paths184, and the cavities180. As a result, the auxiliary bearing system148permits the pads of the friction material164to comply with the excursions of the shaft154, during or after the drop event, while actively damping out vibration. As discussed above, linear, or nearly linear, damping is provided due to the porous fluid communication paths184.

In several exemplary embodiments, during the operation of the auxiliary bearing system148, the fluid in the cavities184facilitate thermal contact with at least the housing170, thereby enhancing heat dissipation. In several exemplary embodiments, the fluid in the cavities184may be fluidically and/or otherwise coupled to an active liquid cooling system to further augment heat dissipation from the pads of the friction material164.

In an exemplary embodiment, as illustrated inFIG. 13, a method of supporting a shaft is generally referred to by the reference numeral190and includes coupling an inertia ring to the shaft wherein the shaft is at least partially disposed in a casing in step190a; compliantly mounting at least two body members to the casing so that each of the body members is permitted to move relative to the casing and the other body members in step190b; supporting the shaft with a primary bearing system in step190c; and engaging the inertia ring with one or more of the compliantly-mounted body members when the primary bearing system fails in step190d.

Although the present disclosure has described embodiments relating to specific turbomachinery, it is understood that the apparatus, systems and methods described herein could applied to other environments. For example, according to another exemplary embodiment, rotating machinery that is driven by a turbomachine may be configured to use embodiments of the auxiliary bearing systems described above.