Foil journal bearing cooling

Cooling is provided for a foil journal bearing by means of flow openings in the individual overlapping foils and/or axially extending slots formed in the high lubricity coating on the surface of the foils.

BACKGROUND OF THE INVENTION 
Process fluid or gas bearings are now being utilized in an increasing 
number of diverse applications. These fluid bearings generally comprise 
two relatively movable elements with a predetermined spacing therebetween 
filled with a fluid such as air, which, under dynamic conditions, form a 
supporting wedge sufficient to prevent contact between the two relatively 
movable elements. 
More recently, improved fluid bearings, particularly gas bearings of the 
hydrodynamic type, have been developed by providing foils in the space 
between the relatively movable bearing elements. Such foils, which are 
generally thin sheets of a compliant material, are deflected by the 
hydrodynamic film forces between adjacent bearing surfaces, and the foils 
thus enhance the hydrodynamic characteristics of the fluid bearings and 
also provide improved operation under extreme load conditions when normal 
bearing failure might otherwise occur. Additionally, these foils provide 
the added advantage of accommodating eccentricity of the relatively 
movable elements and further provide a cushioning and dampening effect. 
The ready availability of relatively clean process fluid or ambient 
atmosphere as the bearing fluid makes these hydrodynamic, fluid film 
lubricated, bearings particularly attractive for high speed rotating 
machinery. While in many cases the hydrodynamic or self-acting fluid 
bearings provide sufficient load bearing capacity solely from the pressure 
generated in the fluid film by the relative motion of the two converging 
surfaces, it is sometimes necessary to externally pressurize the fluid 
between the bearing surfaces to increase the load carrying capability. 
While these externally pressurized or hydrostatic fluid bearings do 
increase the load carrying capacity, they do introduce the requirement for 
an external source of clean fluid under pressure. 
In order to properly position the compliant foils between the relatively 
movable bearing elements, a number of mounting means have been devised. In 
journal bearings, it is conventional practice to mount the individual 
foils in a slot or groove in one of the bearing elements as exemplified in 
U.S. Pat. No. 3,615,121. 
To establish stability of the foils in most of these mounting means, a 
substantial pre-load is required on the foil. That is, the individual 
foils must be loaded against the relatively movable bearing element 
opposed to the bearing element upon which the foils are mounted. It has 
been conventional to provide separate compliant stiffener elements or 
underfoils beneath the foils to supply this required preload as 
exemplified in U.S. Pat. Nos. 3,893,733 and 4,153,315. 
In order to facilitate start-up and to reduce bearing wear, the bearing 
surfaces of the individual foils may be coated with a high lubricity 
material such as a stratified fluorocarbon, molybdenum disulfide, graphite 
fluoride, or the like. The use of such coatings, while enhancing the life 
of the foil bearing, introduces certain operating temperature limitations 
thereon. As still higher temperature environments are envisioned for foil 
bearing operation, the temperature limitations of these coatings become 
critical since they cannot survive as high a temperature as the underlying 
generally metallic foil. Thus, higher temperature coatings must be 
developed or means found to limit the operating temperature at the coated 
foil bearing surfaces. Examples of prior cooling schemes for foil bearings 
can be found in U.S. Pat. Nos. 4,227,753, 4,247,155, and 4,621,930. 
SUMMARY OF THE INVENTION 
In the present invention, the foil journal bearing is provided with 
openings in the individual overlapping foils to enable the flow of cooling 
fluid from beneath the foils to the upper surface of the foils. The 
openings are located in the vicinity of the beginning of the hydrodynamic 
supporting wedge near the overlap from adjacent foils. Where an 
underspring is utilized, the openings should be over a lower ridge so as 
not to restrict the flow of cooling fluid from around the underspring to 
the cooling holes in the individual foils. 
Also, when the overlapping foils are coated with a high lubricity material, 
the coating may be discontinued in the vicinity of the beginning of the 
hydrodynamic supporting wedge near the overlap from adjacent foils to form 
an axially extending slot or slots to promote the axial flow of cooling 
fluid. The foils may include openings therein in association with and in 
proximity to the axially extending slot or slots. 
Since viscous shearing of the fluid film between the bearing foils and the 
rotatable element is a significant source of heating of the coated foil 
surfaces, the supply of cooling flow from underneath the foils and axially 
across the foils at the beginning of the hydrodynamic supporting wedge 
will reduce the operating temperature of the foil journal bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As generally illustrated in FIG. 1, the journal bearing 10 includes a shaft 
12 rotatably supported within a bushing 14 by means of a foil bearing 16. 
The foil bearing 16, shown in FIG. 2, generally comprises a plurality of 
individual, overlapping compliant foils 20 and a like number of individual 
foil stiffener elements or undersprings 22. Both the foils 20 and 
undersprings 22 are mounted in axial slots 24 in the bushing 14 in a 
conventional manner. While the individual curved foils 20, normally of a 
thin compliant metallic material are illustrated as having a separate 
mounting bar 26 at the leading edge thereof, the mounting means may be 
formed integral with the individual foils or with the foils 20 having 
mounting means intermediate the ends thereof as shown in U.S. Pat. No. 
4,178,046. 
The underspring 22, also normally of a thin compliant metallic material, 
generally has a predetermined curvature greater than the curvature of the 
individual foils 20 and includes a plurality of axially extending upper 
ridges 28 alternately disposed with a plurality of axially extending lower 
ridges 30. The function of the undersprings 22 is described in detail in 
U.S. Pat. Nos. 4,153,315 and 4,195,395. 
As best illustrated in FIG. 3, each individual foil 20 includes a plurality 
of cooling holes 32. The holes 32 are generally aligned in an axial row in 
the vicinity of the beginning of the hydrodynamic supporting wedge just 
past the trailing edge 34 of the adjacent overlapping foil as shown in 
FIGS. 2 and 5. In this position, the cooling flow can mix with the bearing 
film flow without adversely affecting the hydrodynamic pressure buildup 
from the relative rotation of the shaft 12 and bushing 14. The diameter of 
the cooling holes 32 may be on the order of 0.1 inches in diameter but may 
range from 0.01 to 0.50 inches. The holes would generally be sized to 
provide sufficient cooling flow to materially reduce the temperature of 
the foil bearing surface without adversely affecting the hydrodynamic 
wedge or the compliance of the individual foils. 
In order to prevent an upper ridge 28 of the underspring 22 from 
restricting the flow of cooling flow through the cooling holes 32, the 
axial row of holes 32 would be positioned, during the operating 
configuration of the foil bearing 16, to be between adjacent upper ridges 
28 as illustrated in FIG. 5. 
The alternate individual foil 20' of FIG. 4, includes two axial rows of 
cooling holes 42, with the cooling holes in the axial row closest to the 
trailing edge of foil 20' generally between the cooling holes in the axial 
row farthest from the trailing edge. Each of the axial rows of cooling 
holes 42 would be disposed over an opening between two upper ridges of the 
underfoil beneath the foil 20' with an upper ridge between the axial rows 
as shown in FIG. 6. 
FIGS. 7 through 13 illustrate an alternate cooling arrangement in which the 
high lubricity material coating on the foils is discontinued in the 
vicinity of the overlap from an adjacent foil to form an axially extending 
slot on the foil. This coating, such as a stratified fluorocarbon, 
polyamide bonded graphite fluoride, or molybdenum disulfide, is provided 
on the foil surface exposed toward the rotating member in order to provide 
a high lubricity surface thereon. 
As illustrated in FIG. 7, the individual foils 50 include suitable mounting 
means such as the mounting bar 58 at one end thereof. The thin compliant 
metallic foil element 52 includes a high lubricity coating 54 thereon. A 
slot 56 is formed on the surface of the foil 50 by removing a portion of 
the coating 54 on the metallic foil element 52. Alternately, the coating 
54 may be formed with the discontinuity or slot 56 thereon when it is 
applied to the metallic foil element 52. 
The individual foil 60 illustrated in FIG. 8 includes a plurality of holes 
62 extending through the foil element 52 in the slot 56. These holes 62 
would normally be in an axial row. As best illustrated in FIG. 9, the 
holes 62 in slot 56 are required to be positioned between adjacent upper 
ridges 28 in the foil stiffener element or underspring 22 beneath the 
individual foils 60. In FIG. 9, the thickness of the coating 54 is 
designated as t.sub.c while the thickness of the overall foil 60 is 
designated as t.sub.f. In order for the cooling flow to be effective in 
the slot 56 it is necessary that the ratio between the coating thickness 
t.sub.c and the foil thickness t.sub.f be at least 1/50 as a minimum. The 
maximum ratio of t.sub.c over t.sub.f can be as high as unity. The slot 56 
is illustrated as being a dimension "a" from the trailing edge 63 of the 
adjacent foil 60 and also as having an arcuate dimension or width of "1". 
In the embodiment illustrated in FIG. 10, the individual foil 64 includes 
an axially extending row of cooling holes 66 upstream of the slot 56. 
These cooling holes 66 extend through both the foil coating 54 and foil 
element 52. The individual foil 68 of FIG. 11 includes an axially 
extending row of cooling holes 70 downstream of the slot 56. These holes 
70 likewise extend through both the coating 54 and foil element 52. FIGS. 
12 illustrates an individual foil 72 having both an axial row of cooling 
holes 62 in the slot 56 and an axially extending row of cooling holes 70 
downstream of the slot 56. The cooling holes 62 in slot 56 would normally 
be axially displaced from the cooling holes 70 downstream of slot 56. 
The plan view of a plurality of overlapping foils illustrated in FIG. 13 
designates the distance between the trailing edges 63 of adjacent foils as 
length "L". The length of the hydrodynamic bearing action zone, which 
provides the hydrodynamic supporting wedge, is designated as "S", while 
the length of the bearing cooling area is designated as "C", (L=S +C). So 
as not to interfere with the hydrodynamic film or supporting wedge, the 
slot 56 and any cooling holes either in the slot 56 or upstream or 
downstream thereof must be disposed in the area before the hydrodynamic 
wedge, namely the bearing cooling area "C". The arcuate width of the slot 
56, "1" and the distance between the trailing edge 63 of the foil 60 and 
the beginning of the slot 56 "a" must be less than "C". To be effective, 
the width of the slot "1" should generally be between 1% to 30% of the 
distance between the trailing edges 63 of adjacent overlapping foils "L". 
Likewise, the distance between the trailing edge 63 of the foil 60 and the 
beginning of the slot 56 should be between zero and 100 times the 
thickness of the foil t.sub.f. 
FIGS. 14-20 illustrate individual foils having two slots in the coating on 
the foils. As shown in FIG. 14, the individual foil 74, having mounting 
means 58, comprises the foil element 76 with a high lubricity coating 78 
thereon. An upstream slot 80 and downstream slot 82 are provided in the 
foil coating 78. 
The individual foil 84 illustrated in FIG. 15 includes a plurality of 
axially extending holes 86 in the upstream slot 80. These holes extend 
through the metallic foil element 76. Likewise, the downstream slot 82 may 
include a plurality of holes 90 as illustrated in FIG. 16. FIG. 17 
illustrates an individual foil 92 having holes 86 in upstream slot 80 and 
holes 90 in downstream slot 82. Holes 86 and 90 would be normally axially 
displaced from the other. 
In addition to holes 86 in upstream slot 80 and holes 90 in downstream slot 
82, the individual foils 94 illustrated in FIGS. 18 and 19 include a row 
of holes 96 between the upstream slot 80 and downstream slot 82. The holes 
96 between the slots 80 and 82 extend through the coating 78 and metallic 
foil element 76. As best illustrated in FIG. 19, the holes 86, 90 and 96 
must each be disposed between adjacent upper ridges 28 of the underspring 
22 so that the upper ridges 28 will not interfere with the flow of cooling 
fluid through these holes. 
FIG. 20 illustrates an individual foil 97 which includes an axial row of 
holes 86 in upstream slot 80, an axial row of holes 90 in downstream slot 
82, an axial row of holes 96 between the upstream slot 80 and downstream 
slot 82, and an axial row of holes 98 downstream of the downstream slot 
82. As was the case with respect to the individual foils having a single 
slot as illustrated in FIGS. 7-13, the plurality of slots 80 and 82 and 
the axially extending rows of holes 86, 96, 90 and 98 must all be in the 
bearing cooling area "C" and thus outside of the area of the supporting 
hydrodynamic wedge "S". The holes should also be axially displaced. 
By providing the axial extending slot(s) in the foil coating, as axial 
cooling flow is established before the hydrodynamic action zone and thus 
is very effective in removing the heat generated in the action zone. In 
combination with cooling holes through the bearing foil, additional 
cooling flow from beneath the foils is also provided. So long as the 
extent and number of slots and holes is limited and only provided in the 
cooling area, all of this can be accomplished without detrimentally 
affecting the hydrodynamic film generation and/or bearing load capacity. 
While specific embodiments of the invention have been illustrated and 
described, it is to be understood that these have been 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.