Thrust bearing assembly with flow path restriction

The present disclosure relates to rotary machines, and in particular, to a thrust bearing in an air cycle machine (“ACM”).

ACMs are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressured air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ACM before the air is delivered to the aircraft cabin.

To condition the air as needed, ACMs include a fan section, a compressor section, and a turbine section that are all mounted on a common shaft. The compressor receives partially compressed air from the aircraft and further compresses the air. The compressed air then moves through a heat exchanger and is cooled by the fan section. The air then moves through the turbine section where it is expanded for use in the aircraft, for example, for use as cabin air. The turbine section also extracts energy from the air and uses the energy to drive the fan section and the compressor section via the common shaft.

ACMs also include bearings that are positioned around the common shaft. The bearings are cooled by passing a cooling air flow through a cavity that is adjacent the bearing. The cooling air flow then exits the cavity and is discharged from the ACM into an ambient environment. The cooling air flow is limited in that it can only cool the bearing using convective heat transfer. Increasing the service life of bearings in ACMs continues to be a goal of designers and manufacturers as failure of these bearings is one of the leading causes for ACM removals.

A bearing assembly includes a shaft and a thrust runner attached to the shaft. The shaft runner protrudes radially outward from the shaft. A thrust bearing is positioned axially adjacent to the thrust runner. A first flow passage is between the thrust runner and a first face of the thrust bearing. A second flow passage is between a second face of the thrust bearing and a housing. A restriction feature restricts a flow of fluid through the second flow passage.

A method of cooling a thrust bearing includes passing a fluid across a thrust bearing through a first flow passage between a thrust runner and a first face of the thrust bearing. Fluid is also passed through a second flow passage between a second face of the thrust bearing and a housing. A flow of the fluid is restricted in the second flow passage at a point along an inner diameter of the thrust bearing. A portion of the flow of the fluid in the second passage is diverted to flow into the first flow passage. The thrust bearing is cooled with the flow of the fluid.

An ACM includes a housing and a thrust runner extending radially outward from a shaft located along a centerline axis of the housing. A thrust bearing is positioned between the housing and the thrust runner. The thrust bearing includes a main plate extending through the thrust bearing. A first flow passage extends along a first face of the thrust bearing. A second flow passage extends between a second face of the thrust bearing and a housing, with the second face being opposite the first face. A restriction feature extends from the housing in an axial direction towards the thrust bearing.

The present summary is provided only by way of example, and not limitation. Other aspects of the present disclosure will be appreciated in view of the entirety of the present disclosure, including the entire text, claims and accompanying figures.

FIG. 1 is a cross-sectional view of an ACM.

FIG. 2 is an exploded perspective view of a thrust bearing of the ACM.

FIG. 3A is a cross-sectional view of a bearing assembly of the ACM according to one embodiment of the present disclosure.

FIG. 3B is a cross-sectional view of a bearing assembly of the ACM according to another embodiment of the present disclosure.

FIG. 3C is a cross-sectional view of a bearing assembly of the ACM according to yet another embodiment of the present disclosure.

While the above-identified figures set forth embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps and/or components not specifically shown in the drawings.

FIG. 1 is a cross-sectional view of ACM 10 , which includes fan section 12 , compressor section 14 , and first stage turbine section 16 . Shaft 20 rotates around central axis 22 . Fan section 12 includes fan blades 24 . Compressor section 14 includes compressor outlet 26 and compressor nozzle 28 . First stage turbine section 16 includes turbine inlet 30 , turbine outlet 32 , and turbine nozzle 34 . FIG. 1 also shows housing 70 , which is discussed with respect to FIGS. 3A-3C as 70 A, 70 B, and 70 C.

Fan section 12 is mounted on shaft 20 . Fan blades 24 rotate around shaft 20 . Fan section 12 is typically used to draw in air from an associated gas turbine engine or other aircraft component.

Compressor section 14 is mounted on shaft 20 . Compressor outlet 26 is a duct through which air can be routed to other systems after it has been compressed in compressor section 14 . Compressor nozzle 28 rotates within in compressor section 14 . In particular, compressor nozzle 28 is a rotor or impeller.

First stage turbine section 16 includes turbine inlet 30 , turbine outlet 32 , and turbine nozzle 34 . First stage turbine section 16 is mounted on shaft 20 . Turbine inlet 30 is a duct through which air passes prior to expansion in first stage turbine section 16 . Turbine outlet 32 is a duct through which air can be routed after it has been expanded to be used in other areas on an aircraft. For example, air can be routed out of turbine outlet 32 and into a cabin for use as cabin air. Turbine nozzle 34 is a nozzle section that extracts energy from air passing through first stage turbine section 16 . In particular, turbine nozzle 34 is a rotor or impeller. Air passing through first stage turbine section 16 drives the rotation of first stage turbine section 16 and any attached components, including shaft 20 , fan section 12 , and compressor section 14 .

Similarly, second stage turbine section 18 includes turbine inlet 36 , turbine outlet 38 , and turbine nozzle 40 . Second stage turbine section 18 is mounted on shaft 20 . Turbine inlet 36 is a duct through which air passes prior to expansion in second stage turbine section 18 . Turbine outlet 38 is a duct through which air can be routed after it has been expanded to be used in other areas on an aircraft. For example, air can be routed out of turbine outlet 38 and into a cabin for use as cabin air. Turbine nozzle 40 is a nozzle section that extracts energy from air passing through second stage turbine section 18 . In particular, turbine nozzle 40 is a rotor or impeller. Air passing through second stage turbine section 18 drives the rotation of second stage turbine section 18 and any attached components, including shaft 20 , fan section 12 , and compressor section 14 .

Shaft 20 is a rod, such as a titanium tie-rod, used to connect other components of ACM 10 . Central axis 22 is an axis with respect to which other components can be arranged.

Air is received in compressor section 14 . The air can be ram air from a ram air scoop or the air can be pulled into ACM 10 using fan section 12 from an associated gas turbine or other aircraft component. The air passes through compressor section 14 where it is compressed with compressor nozzle 28 and then discharged out of compressor outlet 26 . From compressor outlet 26 , the air is then routed into turbine inlet 30 . The air expands as it passes through first stage turbine section 16 and it drives turbine nozzle 34 before it is discharged out of turbine outlet 32 . Air that is discharged out of turbine outlet 32 can then be routed to other parts of the aircraft, for example, for use as cabin air.

Bearing assembly 42 is positioned between first stage turbine section 16 and second stage turbine section 18 . Bearing assembly 42 includes foil thrust bearing 44 , which is shown in isolation in FIG. 2 . Generally, thrust bearings rely on relative rotation between a shaft, typically referred to as the thrust runner, and a bearing to generate a non-linear fluid film between the thrust runner and the bearing. The fluid film forms when the relative rotation of the shaft and bearing interacts with the fluid to create and maintain pressurized wedges of fluid between the shaft and bearing. The pressurized fluid wedge transfers thrust or axial loads from the thrust runner to the bearing, the fluid typically being air or oil. Thrust bearings typically consist of a plurality of bearing foils, also referred to as top foils, and a plurality of bump foils. In a typical arrangement, the plurality of bearing foils and bump foils are welded to the same side of an annular plate, the assembly forming a thrust bearing.

FIG. 2 is an exploded perspective view of foil thrust bearing 44 having axis 46 passing through a geometric center. Foil thrust bearing 44 includes a portion of bearing assembly 42 from FIG. 1 . Axis 46 defines a frame of reference in which an axial direction is parallel with axis 46 , a radial direction is perpendicular to axis 46 , and a circumferential direction corresponds to an angular direction about axis 46 . Foil thrust bearing 44 includes main plate 48 , spacers 50 , bearing foils 52 , and bump foils 54 . Main plate 48 further includes attachment tabs 56 , 56 a , and 56 b and slots 58 , 58 a , 58 b , and 58 c . Main plate 48 provides a structure for mounting spacers 50 , bearing foils 52 , and bump foils 54 . Main plate 48 can be annular in shape.

In general, bearing foils 52 and bump foils 54 attach to opposite faces 60 a and 60 b of main plate 48 , and spacers 50 are arranged between bearing foils 52 and main plate 48 . Bearing foils 52 are provided with clearance between main plate 48 and the outermost face of bearing foils 52 along radially-extending edge 62 to facilitate attachment of bearing foils 52 to main plate 48 . Bearing foils 52 have clearance between adjacent bearing foils 52 that, in some embodiments, is approximate equal to 0.050 inches (0.127 centimeters). Bump foils 54 are corrugated. Spacers 50 can be separate components attached to main plate 48 or be integrally formed with main plate 48 . In either case, spacers 50 can be shaped to support bearing foils 52 in a manner beneficial to the formation of a hydrodynamic fluid film during the operation of foil thrust bearing 44 . For example, spacers 50 can have a generally flat shape that cooperates with bearing foils 52 and bump foils 54 to promote hydrodynamic wedge formation. Foil thrust bearing 44 , bearing foils 52 , and bump foils 54 can include a variety of materials such as nickel-based superalloys and other metal alloys. Foil thrust bearing 44 , bearing foils 52 , and bump foils 54 can also include low friction coatings such as polytetrafluoroethylene.

In the embodiment shown in FIG. 2 , foil thrust bearing 44 has seven spacers 50 , seven bearing foils 52 , and seven bump foils 54 . The number of spacers 50 , bearing foils 52 , and bump foils 54 depend on the size of the bearing and the particular load requirements of the bearing application; however, an odd number for each can be advantageous for detuning the bearing components from natural frequency harmonics of the rotating machine. Higher loads or larger size requirements increase the required bearing area of foil thrust bearing 44 . As the bearing area increases, the number of spacers 50 , bearing foils 52 , and bump foils 54 typically increase in order to limit the portion of the load resisted by any single group of components. In other applications, size limitations can require the number of components to be reduced. Therefore, it will be appreciated by one skilled in the art that the present invention would apply to other thrust bearings having more or less spacers 50 , bearing foils 52 , and bump foils 54 .

Bump foils 54 are in contact with bearing foils 52 . Bearing foils 52 support the air film which carried the thrust load generated by ACM 10 . Heat from the power loss of foil thrust bearing 44 (which can be more than 1 horsepower) is dumped into thrust runner 68 (depicted in FIGS. 3A, 3B, and 3C as 68 A, 68 B, and 68 C respectively) and bearing foils 52 . Cooling flow directed through foil thrust bearing 44 carries off the heat to minimize thermal distortion of thrust runner 68 and bearing foils 52 which can impair bearing capacity. Some of the cooling flow directed through foil thrust bearing 44 passes through a secondary set of bump foils. Although there is a cooling benefit to this secondary airflow it is not as effective as the cooling flow directed through bearing foils 52 .

FIG. 3A is a cross-sectional view of bearing assembly 42 A of ACM 10 according to one embodiment. Bearing assembly 42 A includes thrust bearing 66 A, thrust runner 68 A, and housing 70 A. Thrust bearing 66 A is positioned between thrust runner 68 A and housing 70 A. Thrust bearing 66 A includes main plate 48 A with first face 74 A and second face 76 A positioned on an opposite side of main plate 48 A from first face 74 A. Main plate 48 A also includes outer diameter edge 78 A and inner diameter edge 80 A. First face 74 A includes first foil 82 A and second face 76 A includes second foil 84 A. First flow passage 86 A passes between thrust runner 68 A and main plate 48 A. Second flow passage 88 A passes between main plate 48 A and housing 70 A.

Thrust runner 68 A is connected to shaft 90 A which rotates about a center axis of ACM 10 during operation. Furthermore, thrust runner 68 A rotates relative to thrust bearing 66 A during operation.

First foil 82 A supports an air film which carries a thrust load generated by ACM 10 . Thermal energy from power loss of thrust bearing 66 A (which can be more than 1 horsepower) is transferred to thrust runner 68 A and first foil 82 A. Primary fluid flow 92 A is directed through first flow passage 86 A to transfer thermal energy away from thrust runner 68 A and thrust bearing 66 A to minimize thermal distortion of thrust runner 68 A and first foil 82 A which can impair bearing capacity and overall bearing performance. Additionally, secondary fluid flow 94 A is directed through second flow passage 88 A to draw an additional amount of thermal energy from thrust bearing 66 A. Although there is a cooling benefit to this secondary fluid flow 94 A, secondary fluid flow 94 A is not as effective at thermal energy transfer as primary fluid flow 92 A through first flow passage 86 A. After passing through thrust bearing 66 A, primary fluid flow 92 A and secondary fluid flow 94 A combine to form cooling flow exhaust 96 A which flows out of bearing assembly 42 A.

Secondary fluid flow 94 A is not as effective because it is not directly flowing past first foil 82 A which is heated during use. Primary fluid flow 92 A flows directly along a backside of first foil 82 A. However, for second flow passage 88 A to remove thermal energy, the thermal energy must first be transferred from first foil 82 A to second foil 84 A, and then secondary fluid flow 94 A removes the thermal energy transferred to second foil 84 A. The greater thermal resistance encountered by secondary fluid flow 94 A makes secondary fluid flow 94 A less effective than primary fluid flow 92 A.

Bearing assembly 42 A also includes restriction element 98 A. Restriction element 98 A is in contact with main plate 48 A. Restriction element 98 A forms a seal positioned between housing 70 A and main plate 48 A. Restriction element 98 A can include an O-ring or other type of seal. Restriction element 98 A prevents the secondary fluid flow 94 A from passing inner diameter edge 80 A of main plate 48 A. With secondary fluid flow 94 A being prevented from passing inner diameter edge 80 A of main plate 48 A, a back pressure is created in second flow passage 88 A which diverts secondary fluid flow 94 A to combine with primary fluid flow 92 A, e.g. at or near outer diameter edge 78 A of main plate 48 A, to form cooling flow exhaust 96 A and pass through first flow passage 86 A.

Redirecting secondary fluid flow 94 A into first flow passage increases the overall cooling effectiveness and improved cooling capacity for the same amount of total bearing cooling fluid flow. Because the overall cooling fluid flow across thrust bearing 66 A is metered by downstream shaft orifices, the overall fluid flow rate across thrust bearing 66 A is relatively unchanged while the flow through first flow passage 86 A is as much as doubled.

Bearing assembly 42 A also provides several advantages for ACM 10 . First, bearing assembly 42 A makes ACM 10 more effective, as less cooling air flow is needed to cool thrust bearing 66 A. This means less cooling air flow needs to be routed away from the main flow path through ACM 10 , thus improving the overall efficiency of ACM 10 . The improved efficiency and effectiveness of ACM 10 with bearing assembly 42 A outweighs any concerns about the weight or cost of adding restriction element 98 A to ACM 10 . Bearing assembly 42 A greatly improves the thermodynamic performance of air that is flowing through ACM 10 .

FIG. 3B is a cross-sectional view of bearing assembly 42 B of ACM 10 according to another embodiment. Bearing assembly 42 B includes thrust bearing 66 B, thrust runner 68 B, and housing 70 B. Thrust bearing 66 B is positioned between thrust runner 68 B and housing 70 B. Thrust bearing 66 B includes main plate 48 B with first face 74 B and second face 76 B positioned on an opposite side of main plate 48 B from first face 74 B. Main plate 48 B also includes outer diameter edge 78 B and inner diameter edge 80 B. First face 74 B includes first foil 82 B and second face 76 B includes second foil 84 B. First flow passage 86 B passes between thrust runner 68 B and main plate 48 B. Second flow passage 88 B passes between main plate 48 B and housing 70 B.

Thrust runner 68 B is connected to shaft 90 B which rotates about a center axis of ACM 10 during operation. Furthermore, thrust runner 68 B rotates relative to thrust bearing 66 B during operation.

First foil 82 B supports an air film which carries a thrust load generated by ACM 10 . Thermal energy from power loss of thrust bearing 66 B (which can be more than 1 horsepower) is transferred to thrust runner 68 B and first foil 82 B. Primary fluid flow 92 B is directed through first flow passage 86 B to transfer thermal energy away from thrust runner 68 B and thrust bearing 66 B to minimize thermal distortion of thrust runner 68 B and first foil 82 B which can impair bearing capacity and overall bearing performance. Additionally, secondary fluid flow 94 B is directed through second flow passage 88 B to draw an additional amount of thermal energy from thrust bearing 66 B. After passing through thrust bearing 66 B, primary fluid flow 92 B and secondary fluid flow 94 B combine to form cooling flow exhaust 96 B which flows out of bearing assembly 42 B.

Restriction element 98 B of bearing assembly 42 B includes lip 100 B extending from housing 70 B in an axial direction towards main plate 48 B. Distal end 102 B of lip 100 B is positioned radially inward from inner diameter edge 80 B of main plate 48 B. Distal end 102 B can be aligned in radial direction with main plate 48 B. Spacing X B between distal end 102 B and inner diameter edge 80 B of main plate 48 B in a radial direction can be between 0.002 and 0.020 inches (0.005 and 0.051 cm).

Restriction element 98 B creates a more constricted exit area from second flow passage 86 B than a prior art secondary flow passage without a restriction element. Restriction element 98 B reduces secondary fluid flow 94 B through second flow passage 88 B by up to, and in some instances greater than, 90%. In other words, restriction element 98 B reduces secondary fluid flow 94 B to 10% of what the fluid flow would be in the absence of restriction element 98 B. Restriction element 98 B can also reduce secondary fluid flow 94 B to an amount 90% less than primary fluid flow 92 B.

FIG. 3C is a cross-sectional view of bearing assembly 42 C of ACM 10 according to another embodiment. Bearing assembly 42 C includes thrust bearing 66 C, thrust runner 68 C, and housing 70 C. Thrust bearing 66 C is positioned between thrust runner 68 C and housing 70 C. Thrust bearing 66 C includes main plate 48 C with first face 74 C and second face 76 C positioned on an opposite side of main plate 48 C from first face 74 C. Main plate 48 C also includes outer diameter edge 78 C and inner diameter edge 80 C. First face 74 C includes first foil 82 C and second face 76 C includes second foil 84 C. First flow passage 86 C passes between thrust runner 68 C and main plate 48 C. Second flow passage 88 C passes between main plate 48 C and housing 70 C.

Thrust runner 68 C is connected to shaft 90 C which rotates about a center axis of ACM 10 during operation. Furthermore, thrust runner 68 C rotates relative to thrust bearing 66 C during operation.

First foil 82 C supports an air film which carries a thrust load generated by ACM 10 . Thermal energy from power loss of thrust bearing 66 C (which can be more than 1 horsepower) is transferred to thrust runner 68 C and first foil 82 C. Primary fluid flow 92 C is directed through first flow passage 86 C to transfer thermal energy away from thrust runner 68 C and thrust bearing 66 C to minimize thermal distortion of thrust runner 68 C and first foil 82 C which can impair bearing capacity and overall bearing performance. Additionally, secondary fluid flow 94 C is directed through second flow passage 88 C to draw an additional amount of thermal energy from thrust bearing 66 C. After passing through thrust bearing 66 C, primary fluid flow 92 C and secondary fluid flow 94 C combine to form cooling flow exhaust 96 C which flows out of bearing assembly 42 C.

Restriction element 98 C of bearing assembly 42 C includes lip 100 C extending from housing 70 C in an axial direction towards main plate 48 C. Distal end 102 C of lip 100 C can be aligned in an axial direction with inner diameter edge 80 C of main plate 48 C. Spacing X C between distal end 102 C and inner diameter edge 80 C of main plate 48 C in an axial direction can be between 0.002 and 0.020 inches (0.005 and 0.051 cm).

Restriction element 98 C creates a more constricted exit from second flow passage 86 C than a prior art secondary flow passage without a restriction element. Restriction element 98 C reduces secondary fluid flow 94 C through second flow passage 88 C by up to, and in some instances greater than, 90%. In other words, restriction element 98 C reduces secondary fluid flow 94 C to 10% of what the fluid flow would be in the absence of restriction element 98 C. Restriction element 98 C can also reduce secondary fluid flow 94 C to an amount 90% less than primary fluid flow 92 C.

Generally, restriction elements 98 A, 98 B, and 98 C cause a flow area of second flow passages 88 A, 88 B, and 88 C to be locally reduced, thereby creating an at least partial seal that redirects secondary fluid flows 94 A, 94 B, and 94 C due to back pressure formed in second flow passages 88 A, 88 B, and 88 C.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments of the present invention.

A bearing assembly can include a shaft and a thrust runner attached to the shaft. The shaft runner can protrude radially outward from the shaft. A thrust bearing can be positioned axially adjacent to the thrust runner. A first flow passage can be between the thrust runner and a first face of the thrust bearing. A second flow passage can be between a second face of the thrust bearing and a housing. A restriction feature can restrict a flow of fluid through the second flow passage.

The bearing assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

a further embodiment of the foregoing bearing assembly, wherein the thrust bearing may comprise a main plate with an annular shape and that can be located between the first and second faces of the thrust bearing, wherein the main plate can include an outer diameter edge and an inner diameter edge;

a further embodiment of any of the foregoing bearing assemblies, wherein the first face of the thrust bearing can comprise a first plurality of top foils, a first plurality of bottom foils, and further wherein the second face of the thrust bearing can comprise a second plurality of top foils and a second plurality of bottom foils;

a further embodiment of any of the foregoing bearing assemblies, wherein the restriction feature can comprise a lip extending towards the second face of the thrust bearing in an axial direction;

a further embodiment of any of the foregoing bearing assemblies, wherein a distal end of the lip is can be positioned radially inward from the main plate inner diameter edge and in radial alignment with the main plate of the thrust bearing;

a further embodiment of any of the foregoing bearing assemblies, wherein a distal end of the lip can be positioned in axial alignment with the main plate inner diameter edge;

a further embodiment of any of the foregoing bearing assemblies, wherein the restriction feature can further comprise an O-ring positioned between a second face of the thrust bearing and a housing; and/or

a further embodiment of any of the foregoing bearing assemblies, wherein the O-ring can be positioned in axial alignment with the main plate inner diameter edge, and further wherein the O-ring can be in contact with the main plate.

A method of cooling a thrust bearing can include passing a fluid across a thrust bearing through a first flow passage between a thrust runner and a first face of the thrust bearing. Fluid can be passed through a second flow passage between a second face of the thrust bearing and a housing. A flow of the fluid can be restricted in the second flow passage at a point along an inner diameter of the thrust bearing. A portion of the flow of the fluid in the second passage can be diverted to flow into the first flow passage. The thrust bearing can be cooled with the flow of the fluid.

The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

a further embodiment of the foregoing method can further comprise positioning the thrust bearing axially adjacent the thrust runner;

a further embodiment of any of the foregoing methods, wherein restricting a flow of air in the second flow passage further can include positioning a restriction feature along the thrust bearing; and/or

a further embodiment of any of the foregoing methods, wherein diverting a portion of the flow of the fluid in the second passage can further comprise creating a back pressure in the second passage.

An ACM can include a housing and a thrust runner extending radially outward from a shaft located along a centerline axis of the housing. A thrust bearing can be positioned between the housing and the thrust runner. The thrust bearing can include a main plate extending through the thrust bearing. A first flow passage can along through a first face of the thrust bearing. A second flow passage can extend between a second face of the thrust bearing and a housing, with the second face being opposite the first face. A restriction feature can extend from the housing in an axial direction towards the thrust bearing.

The ACM of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

a further embodiment of the foregoing ACM, wherein the main plate can comprise an annular shape and can be located between the first and second faces of the thrust bearing, wherein the main plate can include an outer diameter edge and an inner diameter edge;

a further embodiment of any of the foregoing ACMs, wherein the first face of the thrust bearing can comprise a first plurality of top foils and a first plurality of bottom foils, and further wherein the second face of the thrust bearing can comprise a second plurality of top foils and a second plurality of bottom foils;

a further embodiment of any of the foregoing ACMs, wherein the restriction feature can comprise a lip extending from the housing in an axial direction;

a further embodiment of any of the foregoing ACMs, wherein a distal end of the lip can be positioned radially inward from the main plate inner diameter edge and in radial alignment with the main plate of the thrust bearing;

a further embodiment of any of the foregoing ACMs, wherein a distal end of the lip can be positioned in axial alignment with the main plate inner diameter edge;

a further embodiment of any of the foregoing ACMs, wherein the restriction feature can further comprise an O-ring positioned between the housing and the second face of the thrust bearing; and/or

a further embodiment of any of the foregoing ACMs, wherein the O-ring can be positioned in axial alignment with the main plate inner diameter edge, and further wherein the O-ring is in contact with the main plate.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.