Table of Contents. Previous article Next article. Article Abstract PDF 3. Metrics Show article metrics. Services Articles citing this article CrossRef Bookmarking Mendeley. Reader's services Email-alert. After cooling the journal bearing 38, the air then exits the turbogenerator 10 in the exhaust gas stream as shown by the arrows in FIG. In addition, some bleed air is vented radially inward recirculated through the space between the thrust plate 42 and bearing rotor thrust disk 37, this space functioning as a variable orifice, and radially outward through the space between the thrust plate 42 and the back of the compressor wheel The thrust bearing fluid foil member 48 and thrust bearing spring foil member 49, including three 3 spring foil elements 60, 61, and 62, are disposed on either side of the bearing rotor thrust disk On the turbine side, the fluid foil member 48 and spring foil member 49 are positioned on the thrust face 46 of the center bearing housing 39 and on the compressor side they are adjacent to the thrust plate It should be recognized that the space between the thrust bearing plate 42 and the bearing rotor thrust disk 37 and the space between the bearing rotor thrust disk 37 and the thrust face 46 of the center bearing housing 39 is shown as enlarged for purposes of illustration.
A cooling air passage 58 may extend from the base of the turbine side of the bearing rotor thrust disk 37 to the compressor end of the bore in the bearing rotor In addition, a cooling air vent 59 may be included in the turbine end thinned down section of the bearing rotor 36 to allow the flow of cooling air to traverse the bearing rotor 36 and exit adjacent to the heat shield The thrust bearings would be of the compliant foil hydrodynamic fluid film type of bearing, an example of which can be found in U. Likewise, the journal bearings should be of the compliant foil hydrodynamic fluid film type of bearing.
An example of this type of bearing is described in detail in U.
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A like plurality of radial end slots 91 connect the peripheral slots 90 with the interior of the journal bearing cartridge 38'. Each end of the cartridge 38' is cut back to form smaller diameter ends 92 and The slots 90 and 91 and smaller diameter ends 92 and 93 together facilitate the flow of compressor air from the compliant foil hydrodynamic fluid film thrust bearing around the journal bearing cartridge 38' and provide substantial cooling of the bearing cartridge 38' and bearing rotor The slots 90 and 91 can also function as fixed orifices to control the hydrostatic augmentation of the thrust bearing.
An exploded end view of a portion of the cartridge 38' is shown in FIG. The fluid foil member 54 and spring foil member 55 are shown in the bore of the cartridge 38' near a diverging ramp An enlarged generally arcuate cavity 75 communicates with the bore of the cartridge 38' by means of a radial slot 76 near the base of the diverging ramp The arcuate cavity may be larger towards the diverging ramp 72 since that will normally be the hottest area of the bore. An arcuate cavity 75 may be located at each intersection of the base of a diverging ramp 72 and the beginning of the next converging ramp, but not at the preload bar where there is already greater clearances for cooling air flow.
These arcuate cavities 75 can be produced with a small EDM entry slot which is then enlarged beyond the slot width. Although the area at the base of the diverging ramps 72 would be the preferred location for the slot 76 and cavity 75, they can also be situated at other locations around the bore. A bore liner might, however, be required at other locations to prevent the cantilever beam from getting into a slot The thrust face 44 of the thrust plate 42 is shown in detail in the exploded perspective of FIG.
The plurality of radially extending orifices 41 are shown spaced around the periphery 47 of the thrust plate As best illustrated in FIG. The feeder holes 43 provide bleed air from the radially extending orifices 41 to the arcuate channels Each arcuate channel 56 may be supplied by a single feeder hole 43 or there may be a plurality of feeder holes for each arcuate channel In FIG. The number of feeder holes 43 can be selected based upon bleed air flow and distribution requirements.
The bleed air distributed by the channels 45 in the thrust face 44 of the thrust plate 42 flows through the thrust bearing spring foil member 49 which consists of outer support foil 60, spring foil element 61, and inner support foil 62 before acting upon the fluid foil member The fluid foil member 48, best illustrated in FIG. The fluid foil member 48 would normally be annealed both during forming and use and may be coated prior to forming the joggles with any number of a myriad of low friction or friction reducing coating materials which can protect the metal from abrasion during starting and stopping, and inadvertent and occasional high speed touch-downs.
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The coating would also provide for some imbedment of contamination particles. The fluid foil member 48 includes a plurality of individual fluid foil pads 65 which are generally chevron shaped and connected to an outer self shimming ring 68 by support webs Each fluid foil pad 65 has a trailing edge 71 with a rounded trailing point and a leading edge A generally scoop shaped hydrodynamic converging ramp 73 is formed with a generally straight ramped contour from the leading edge 74 to the trailing edge 71 and a rounded concave contour from the circumferential line of the trailing edge 71 to the outer diameter of the fluid foil pad 65 and to the inner diameter of the fluid foil pad As best illustrated in the two sectional views of FIGS.
On the compressor side of the bilateral compliant foil hydrodynamic fluid film thrust bearing, a plurality of air flow orifices 77 are arranged at the base or beginning of each of the hydrodynamic converging ramps 73 of the fluid foil pads The air flow orifices 77 allow the bleed air that has passed through the spring foil members 49 to pass through the fluid foil member 48 to apply a force against the compressor side face of the bearing rotor thrust disk 37 and establish a hydrostatic bearing function. The pressure drop across air flow orifices 77 establishes an air spring function supporting the fluid foil pads 65 of the fluid foil member Both the hydrostatic bearing function and the hydrostatic spring function drive the bearing rotor thrust disk 37 towards the turbine.
When the bearing rotor thrust disk 37 moves towards the turbine, more air bleeds outward and over the bearing rotor thrust disk 37 and around the turbine side thrust bearing and more air bleeds inward and between the compressor wheel back plane and thrust plate 42 causing the force exerted on the thrust disk surface to be somewhat diminished. The initial axial thrust from the hydrostatic bearing function and the hydrostatic spring function will be reduced until it nearly matches and opposes the net thrust of the compressor and turbine wheels.
The turbine side of the compliant foil hydrodynamic fluid film thrust bearing will be conventional without the air flow orifices in the fluid foil pads. Bleed air flowing through the spring foil members 49 and the fluid foil member 48 on the compressor side of the bearing rotor thrust disk 37 causes the fluid foil member 48 to deflect towards the bearing rotor thrust disk 37 and causes the bearing rotor thrust disk 37 to move towards the turbine Movement of the bearing rotor thrust disk 37 towards the thrust plate 42 and the compressor 30 will serve to increase the hydrostatic forces on the compressor side of the bearing rotor thrust disk 37 by narrowing the flow vent path for the bleed air out of the thrust bearing.
Since the compressor discharge pressure varies with the square of turbomachine speed, the hydrostatically generated thrust forces will also be proportional to the square of turbomachine speed.
Also, the hydrostatically generated thrust forces will be a function of the axial position of the bearing rotor thrust disk The flow of bleed air through the compliant foil hydrodynamic fluid film thrust bearing will be affected by the axial position of the bearing rotor thrust disk 37 and this relative position will serve as a variable orifice flow control of the bleed air used to attenuate the hydrostatically generated thrust forces.
The hydrostatic and hydrodynamic thrust bearing forces cooperate and function integrally together. The fixed orifices of the compliant foil hydrodynamic fluid film journal bearing will work in series with the variable orifices of the compliant foil hydrodynamic fluid film thrust bearing to jointly control the differential pressure across the rotating bearing thrust disk and the resulting hydrostatic thrust bearing force. The left arrow identified as A represents compressor wheel static pressure discharge before the compressor diffuser. This pressure would be on the order of nineteen 19 to twenty-four 24 psig.
The fixed orifice 80 represents the radially extending orifices 41, the axially extending feeder holes 43, and channels 45, all in the thrust plate 42 together with air flow orifices 77 in the fluid foil pad Pressure arrow B, on the order of sixteen 16 psig is directed to the thrust disk 37 and to the thrust bearing variable orifices 82 and then to the bypass passages 83 around the turbine side thrust bearing before reaching pressure arrow C, which is on the order of eight 8 psig.
Since the bearing rotor thrust disk will be moved axially by the net aerodynamic and hydrostatic thrust forces acting thereon, the orifices 82 are indeed variable. When the bearing rotor thrust disk is moved to the left by these net thrust forces, the hydrostatic pressure on the left or compressor side of the bearing rotor thrust disk 37 will be increased, thus effectively balancing the net thrust forces. The variable orifices 82, interacting with the fixed orifices, effectively control the level of balancing hydrostatic thrust forces that are generated.
The differential pressure across the rotating bearing rotor thrust disk 37, and thus the hydrostatic thrust forces, are a function of the axial position of the bearing rotor thrust disk The variable orifices 82 represent the distance between the thrust bearing fluid foil member 48 and the bearing rotor thrust disk The bleed air then proceeds around and through the compliant foil hydrodynamic fluid film journal bearing represented by fixed orifices 85, 86, and 87 before reaching a pressure on the order of four 4 psig at arrow D.
In addition to the variable orifices 82, the downstream fixed orifices 85, 86, and 87 will also impact the differential pressure across the rotating bearing rotor thrust disk 37 and will function in concert with the variable orifices Fixed orifice 85 represents the flow of cooling air between the bearing cartridge 38' and the center bearing housing 39, fixed orifice 86 represents the flow of cooling air through the bearing cartridge 38', including slots 90 and 91 and arcuate cavities 75, and fixed orifice 87 represents the flow of cooling air between the bearing rotor 36 and the tie bar As best shown in FIG.
The pressures stated above would be typical for full speed operation of the turbomachine and would obviously be less for partial speed operation. Pressure in pounds per square inches psig is plotted against axial deflection of the bearing rotor thrust disk 37 from center location in inches in FIG. Line A represents the pressure at point A, line B represents the pressure at point B, line C represents the pressure at point C, and line D represents the pressure at point D.
The distance between lines B and C represents the pressure differential across the bearing rotor thrust disk While specific embodiments of the invention have been illustrated and described, it is to be understood that these are provided by way of example only and that the invention is not to be construed as being limited thereto but only by the proper scope of the following claims.
Effective date : Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : A system to hydrostatically augment the thrust load capacity of a bilateral compliant foil hydrodynamic fluid film thrust bearing for a turbomachine is disclosed. A plurality of channels and fixed orifices are provided in the bearing thrust plate to deliver and regulate compressor bleed air flow to the compressor side of the bilateral compliant foil hydrodynamic fluid film thrust bearing which includes additional channels and orifices to direct the bleed air against the bearing rotor thrust disk.
After impinging on the rotor thrust disk, the bleed air flow exits the thrust bearing through a plurality of variable orifices comprised of the hydrodynamic thrust bearing elements which are controlled in their flow conductance by the axial position of the rotor thrust disk.
The bleed air may then pass through the adjacent journal bearing which functions as a fixed orifice. The interaction of the fixed orifices and variable orifices establishes a pressure differential across and a net force applied to the bearing rotor thrust disk that varies as a function of the axial position of the bearing rotor thrust disk. Further, the bleed air from the bearing rotor thrust disk being delivered to the compliant foil hydrodynamic fluid film journal bearing of the turbomachine serves to cool the journal bearing.
TECHNICAL FIELD This invention relates to the general field of compliant foil hydrodynamic fluid film thrust bearings and more particularly to an improved system that utilizes hydrostatically generated forces to augment the load bearing capacity of one side of a two-sided or bilateral compliant foil hydrodynamic fluid film thrust bearing. SUMMARY OF THE INVENTION In the present invention, the unequal loading of the opposite sides of a bilateral compliant foil hydrodynamic fluid film thrust bearing is reduced or eliminated by hydrostatically augmenting one side of the bilateral compliant foil hydrodynamic fluid film thrust bearing with bleed air from the compressor which is rotatably supported by the bilateral compliant foil hydrodynamic fluid film thrust bearing and compliant foil hydrodynamic fluid film journal bearings.
What we claim is: 1. The bearing case end cover 42 is joined to the bearing case 40 by connectors The bearing case end cover 42 abuts stationary bearing support 18 to which is fitted journal bearing pad 32 and thrust bearings 24, 26, 28, Bearing connector 36 connects journal bearing pad 32 to bearing support The rotatable rotor or shaft 12 is hollowed out creating cavity 14 and central spindle 16 onto which is fitted bearing support Journal bearing pads 32 are located between bearing support 18 and the outer wall of shaft cavity Thrust collar 20 is fitted against the terminal end of the rotor spindle 16 and secured in place by nut Thrust bearing pads 24, 26 are fixably attached to the bearing support 18 and positioned between bearing support 18 and thrust collar Seal 46 is placed into channel 52 in bearing support Seal 48 is placed into channel 49 in bearing support 18 and fitted circumferentially against the outer edge of thrust collar Thrust bearing pads 28, 30 are attached preferably loosely to bearing support 18 with positioning pins not shown anchored in the bearing support and extending into holes made in the thrust bearings to receive such pins.
Thrust bearing pads 28, 30 are positioned between bearing support 18 and the outer wall of shaft cavity The turbomachine 60 has an exhaust end 62 and an inlet end Turbomachine casing 66 houses the rotating turbine wheel or rotor 68 which is attached to the turbomachine shaft 12, and the stationary diaphragm 70 located between turbine wheels At one end of the turbine opposite the exhaust end is located the inlet end bearing case 10 which houses the journal bearing assembly as shown in FIGS. The journal bearing pads located inside the end of the hollowed out shaft 12, and the thrust bearings are partially visible in this view.
Each bearing pad preferably is arcuate in configuration and includes a leading edge and a trailing edge. The pad is positioned such that its outer convex surface closely matches the concavity of the shaft cavity wall. The leading edge of the journal bearing pad is defined as the edge first approached by a point on the circumference of the shaft as it continues to rotate. Similarly, the trailing edge is defined as the edge approached circumferentially later by the same point on the shaft as it continues to rotate.
When the shaft is rotating in the proper direction, it moves, on a fluid film, from the leading edge across the bearing pad and off the trailing edge. Although specific reference is made to either journal bearings or thrust bearings to facilitate an understanding of the invention, some of the same principles apply regardless of the specific form of the bearing being designed. For example, both journal and thrust bearings operate on the principle of formation of a hydrodynamic wedge.
However, there are also significant differences between thrust and journal bearings. For instance, while journal bearings support circumferential portions of shafts, thrust bearings support shoulder or axial end portions of shafts.go
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Other differences follow from this fundamental difference. For example, in a radial or journal bearing the pads in the direction of the load take or support the load.
In a thrust bearing, all pads normally share load. Moreover, a journal bearing generally has a built-in wedge due to differences in the shaft and bearing diameters. There may be no such built-in wedge in thrust bearings.
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Additionally, while a journal or radial bearing controls rotational stability as well as load, a thrust bearing typically only carries load. Bearing pads may be babbitted or not and are made from a variety of materials such as carbon steel, stainless steel, bronze, copper alloys, ceramic, ceramic composites, plastics, and preferably lead-tin babbitted steel alloy pads. The lead-tin babbitted steel alloy pads are preferred for use in turbomachines. Babbitted pads are understood to be pads incorporating a thin layer of material such as lead-tin preferably heat-bonded to the metal pad.
These pads are rigid enough to support the journal load, and possess adequate heat transfer properties to transmit the heat created in the fluid film during operation. Such pads also provide adequate coefficients of friction for initial rotation breakaway and are commercially available. A lubricant fluid is provided to the bearing assemblies as a natural or synthetic lubricating oil or other hydraulic fluid lubricant as would be conventionally used for lubricating such systems. The fluid is provided under relatively low pressure, for example about 25 psi, to the bearing assembly via piping not shown in the diagrams, but which would be readily understood by those skilled in the field of bearings and turbomachine operation.
The fluid is retained in the system by appropriately positioned seals, such as ring seals which guard against leakage.
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