Fluid foil bearing

A fluid foil bearing comprises a bearing housing in which the journal of a rotatable shaft is positioned, a single foil bearing is so arranged in the housing as to surround substantially the whole circumference of the shaft journal with a minute space interposed between the foil bearing and the shaft journal, and supporting under foils are disposed outside the foil bearing and inside the housing for resiliently supporting the foil bearing at circumferentially spaced intervals so as to provide a predetermined preload on the shaft.

BACKGROUND OF THE INVENTION 
This invention relates to a fluid foil bearing of the journal or radial 
type. 
One known fluid foil bearing of this type comprises a plurality of thin 
resilient metal sheets or foils so arranged in the bearing housing as to 
surround a rotatable element or shaft to be supported by the bearing, so 
that as the shaft is rotated, a dynamic pressure of the fluid developed in 
the wedge-shaped spaces formed between the opposed surfaces of the foils 
and the shaft provides a bearing effect for the shaft floating in the 
fluid between the foils and the shaft. Since this bearing is of a 
non-contact type, it is substantially free from overheating, enables 
rotation of the shaft at a higher speed than otherwise and is suitable for 
use in various pneumatic machines such as turbines. 
The provision of many separate foils within a narrow space between the 
inner circumferential surface of the bearing housing and the outer 
circumferential surface of the rotatable shaft, however, makes the 
structure of the bearing complex and bulky, and it is also difficult with 
the prior art arrangement to adjust the stiffnesss or spring constant of 
the foils. 
If the foils are so arranged that they partially overlap each other, it is 
less likely that wedge-shaped spaces are formed between the outer 
circumferential surface of the shaft and the opposed surfaces of the 
foils, and it becomes difficult to adjust the pressure with which the 
foils contact the shaft, that is, the preload exerted on the shaft by the 
foils, so that bearings of different characteristics and capacities must 
be provided to provide different amounts of preload. 
Accordingly, it is a general object of the invention to provide an improved 
fluid foil bearing which is free from the above-mentioned and other 
disadvantages of the prior art arrangements. 
Another object of the invention is to provide an improved fluid foil 
bearing which is easy in adjustment of preloading of the shaft. 
Another object of the invention is to provide an improved fluid foil 
bearing which is simple in construction, and reliable and accurate in 
operation. 
The invention will be described in detail with reference to the 
accompanying drawings.

SUMMARY OF THE INVENTION 
The invention provides a fluid foil bearing which comprises a bearing 
housing and a single sheet of resilient foil disposed in the housing to 
function as a bearing element for a rotatable element such as the shaft of 
a turbine. The bearing foil which will also be referred to as the upper 
foil is anchored along one side edge thereof to the interior surface of 
the bearing housing by means of an anchoring pin fitted into a 
corresponding slot or channel formed in the interior surface of the 
bearing housing. 
The bearing foil extends from the anchoring pin so as to surround 
substantially the whole outer circumferential surface of the shaft, with a 
plurality of resilient supporting elements or under foils disposed between 
the outer circumferential surface of the single bearing foil and the 
interior surface of the bearing housing to resiliently support the bearing 
foil at circumferentially spaced intervals thereby to provide an 
appropriate preload on the shaft. The arrangement enables easy adjustment 
of preloading. 
As the shaft is rotated, a dynamic pressure developed in the wedge-shaped 
spaces formed between the shaft and the bearing foil provides an efficient 
fluid bearing effect for the rotating shaft. 
The invention provides another fluid foil bearing which comprises a bearing 
housing and a plurality of resilient bearing foils so arranged in the 
housing as to surround a rotatable shaft. The bearing foils are so 
dimensioned that they do not overlap each other, and are cantilevered at 
one side edge thereof to the interior surface of the housing at 
circumferentially spaced intervals, with a resilient supporting element or 
under foil underlying each of the upper bearing foils to resiliently 
support the bearing foil adjacent the middle portion thereof thereby to 
provide an appropriate amount of preload on the shaft. 
Each of the under foils is also cantilevered to the interior surface of the 
bearing housing immediately adjacent the position where the corresponding 
upper bearing foil is anchored. The arrangement simplifies the structure 
of the bearing and enables easy adjustment of preloading of the shaft. 
The invention provides a third fluid foil bearing which comprises a bearing 
housing and a plurality of bearing elements so arranged in the housing as 
to surround a rotatable shaft. The bearing elements are generally T-shaped 
in cross section and comprises a relatively short central leg and a pair 
of wings made of resilient foil and extending from the leg in opposite 
directions circumferentially of the shaft. 
The bearing elements are anchored at the central leg thereof to the 
interior surface of the bearing housing at circumferentially spaced 
intervals, with the opposite wings of each of the bearing elements 
partially overlapping the adjacent wings of the adjacent bearing elements. 
The overlapping wing portions are resiliently supported by a supporting 
element so that a predetermined preload is imposed on the shaft. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings wherein the same reference numerals or 
symbols in different figures designate corresponding parts or elements, 
there is shown in FIG. 1 a turbine rotor 10 fixedly carried by a rotatable 
shaft 11 having opposite journals supported by a pair of fluid foil 
bearings 12. The two bearings are of the same construction, so that only 
one of them will be explained. 
FIG. 2 shows the interior mechanism of the bearing 12 in transverse cross 
section, with the shaft 11 shown in the state of rotation. 
The bearing 12 comprises a bearing housing 13, a single bearing foil 14 and 
six supporting foils 15.sub.1 to 15.sub.6. The bearing foil 14 will be 
referred to also as the upper foil and the supporting foils 15.sub.1 to 
15.sub.6, as the under foils. Since the six under foils are of the same 
structure, they will be designated by 15 without the suffix when no 
discrimination is needed. 
The bearing housing 13 is mounted on a suitable fixed member or frame of 
the pneumatic machine, not shown. 
The bearing foil 14 and the supporting foils 15 may be of any suitable 
material such as stainless steel having a suitable resiliency and a 
sufficient resistance to wear which would occur in fluid foil bearing 
operation. The bearing foil 14 has an elongated rectangular shape of a 
suitable size. An anchoring pin 14a of rectangular cross section is fixed 
to one side edge of the bearing foil 14 in any suitable known manner such 
as spot welding. 
The bearing housing 13 is formed in the interior surface thereof with six 
slots or channels 16.sub.1 -16.sub.6 extending a predetermined length in a 
direction parallel to the axis of the housing 13 and arranged at 
60.degree. spaced intervals circumferentially thereof. The channel 
16.sub.1 is of a width greater than that of the other channels 16.sub.2 
-16.sub.6. 
The anchoring pin 14a of the bearing foil 14 is fitted into the channel 
16.sub.1 and extends therefrom counterclockwise in FIG. 2 substantially 
the whole circumference of the shaft 11 as far as it terminates in a free 
end 14' above and adjacent the anchoring pin 14a. The width of the bearing 
foil 14 longitudinal of the shaft 11 depends on the axial length of the 
journal of the shaft. 
It should be noted that the illustrated relative dimensions of the parts or 
elements as well as those of the gaps or spaces in the figures do not 
represent the actual dimensions. In particular, the thickness of the foils 
and the distance of the gap or space between the foil or foils and the 
shaft or the interior surface of the housing are shown exaggerated only 
for simplicity and clarity of illustration. 
The under foils 15.sub.1 to 15.sub.6 are of a rectangular or square shape 
having a shorter length than the upper foil 14 in the circumferential 
direction of the shaft 11, and each of the under foils has its one edge 
fixed to an anchoring pin 15a similar to the anchoring pin 14a of the 
bearing foil 14. The under foils 15.sub.1 to 15.sub.6 are arranged around 
the upper bearing foil 14, with the anchoring pins 15a being detachably 
fitted into the corresponding channels 16.sub.1 to 16.sub.6, so that the 
under foils resiliently support the upper foil 14 at six positions spaced 
60.degree. apart from each other circumferentially of the upper foil or 
the shaft, thereby causing the upper foil to contact the shaft with a 
suitable contact pressure or preload. 
Although in the illustrated embodiment of FIG. 2 the anchoring pin 15a of 
the under foil 15.sub.1 is fitted into the same channel 16.sub.1 into 
which the anchoring pin 14a of the upper foil 14 is fitted, the two pins 
14a and 15a may be fitted into separate channels. 
In FIG. 2 the under foils 15.sub.1 to 15.sub.6 are so arranged in the 
bearing housing 13 that they extend from their respective anchoring pins 
15a counterclockwise, that is, in the same direction as that of rotation 
of the shaft 11. The arrangement may also be such that the under foils 
extend from the anchoring pin clockwise, that is, in the direction 
opposite to that of rotation of the shaft as shown in FIG. 2a, wherein the 
same reference numerals as in FIG. 2 designate corresponding parts so that 
no further explanation will be needed. 
As the shaft 11 is rotated counterclockwise as indicated by an arrow in 
FIG. 2 or 2a, the shaft is in contact with the bearing foil 14 due to the 
preload caused by the under foils 15.sub.1 to 15.sub.6 until a 
predetermined rotational speed e.g. 1000 r.p.m. is reached, whereupon a 
dynamic pressure is produced in the six wedge-shaped spaces not shown but 
formed between the outer circumferential surface of the shaft 11 and the 
opposed inner circumferential surface of the bearing foil 14 to cause the 
shaft to float within the space defined by the bearing foil, so that the 
shaft can be rotated at a higher speed of e.g. 100,000 r.p.m. 
While the shaft is being rotated at a high speed, if an abnormal condition 
occurs to displace the shaft, the bearing and supporting foils are 
displaced and/or deformed so that the bearing space between the shaft and 
the bearing foil is kept constant thereby to keep the bearing function 
stable and steady. 
The preload on the shaft provided by the under foils is determined 
depending upon the masses of the shaft and the rotor of the turbine and 
the amount of load to be carried by the turbine. The preload can be 
adjusted or changed by changing the number of the under foils provided 
(e.g. by providing five instead of six under foils with one under foil 
having been removed) or by changing the dimensions and/or material of the 
under foils thereby to change the stiffness or spring constant thereof. 
Since there is provided only a single bearing foil, the number of the 
component parts of the bearing is reduced, so that the whole structure of 
the bearing is simplified and made compact. The bearing foil 14 may have a 
desired thickness within a predetermined range, and the thickness need not 
be determined with a high degree of accuracy, with resulting easiness in 
making the foil. When the shaft 11 is displaced during rotation for one 
cause or another, the resilient under foils 15 allow the upper bearing 
foil 14 to be displaced and/or deformed to ensure a stable bearing 
function. Even when foreign bodies happen to be introduced into the 
bearing space, the dynamic pressure will not be reduced but kept 
substantially unchanged so that a stable bearing function is maintained. 
By selecting the design of the under foils it is easily possible to provide 
a fluid foil bearing suitable for a particular application. Since 
considerable tolerances are allowed in the design and dimensions of the 
foils, the fluid foil bearing of the invention is suitable for mass 
production. the bearing is free from thermal strain and suitable for high 
speed operation and can endure long use and improve the performance of the 
pneumatic machines in which the bearing is used. 
FIGS. 5 and 6 show another embodiment of the invention, wherein there are 
provided four upper bearing foils 17.sub.1 to 17.sub.4 and four 
corresponding under supporting foils 18.sub.1 to 18.sub.4 each paired with 
one of the bearing foils. 
Each of the upper foils 17.sub.1 to 17.sub.4 is cantilevered at one side 
edge thereof to an anchoring pin 17a, to which the under foil paired with 
the upper foil is cantilevered at the corresponding one side edge thereof. 
The anchoring pins 17a of the four pairs of upper and under foils are 
detachably fitted respectively into four slots or channels 16.sub.1 to 
16.sub.4 formed in the interior surface of the bearing housing 13 at 
90.degree. spaced intervals circumferentially thereof, so that the upper 
foils surround the shaft 11, with the under foils resiliently supporting 
the upper foils adjacent the middle portion thereof and causing them to 
contact the shaft with a certain pressure or preload. 
The upper foils 17.sub.1 to 17.sub.4 are of such shape and size that they 
do not overlap each other. The length of the upper foils in the direction 
of rotation of the shaft depends on the number of foils provided. In the 
illustrated embodiment, since there are provided four foils, their length 
approximates the length of one side of a square circumscribing the shaft 
11. The length of the under foils is a little smaller than that of the 
upper foils. 
The width of the upper and under foils longitudinal of the shaft 11 depends 
upon the axial length of the journal of the shaft. 
The magnitude of preload provided by the under foils is determined by the 
resiliency of the foils and can be adjusted or changed by changing the 
number of the pairs of upper and under foils provided and/or the size, 
shape or material of the foils. 
As the shaft is rotated at above a predetermined speed, the dynamic 
pressure developed in the four wedge-shaped spaces formed between the 
outer circumferential surface of the shaft and the four bearing foils 
provides a fluid bearing for the shaft to enable stable high speed 
rotation of the shaft. Any displacement of the rotating shaft may be 
compensated by such deformation or displacement of the foils as to keep 
constant the bearing space between the shaft and the bearing foils. 
Since the upper bearing foils do not overlap each other but are supported 
by individual under supporting foils, it is easy to adjust the preload 
imposed on the shaft by changing the size, shape and material of the under 
foils. The arrangment of the piled upper and under foils combined with a 
common anchoring pin makes the structure of the bearing simple and compact 
and suitable for high speed bearing operation. 
Turning now to FIGS. 7 to 9 which show a third embodiment of the invention, 
there are shown four bearing elements 19.sub.1 to 19.sub.4 which are 
generally T-shaped in cross section and comprise a relatively short 
central leg 19a and a pair of wings 19L and 19R made of resilient foil and 
extending from the leg 19a laterally in opposite directions and being 
upwardly curved. In the interior surface of the bearing housing there are 
formed four slots or channels 16.sub.1 to 16.sub.4 spaced 90.degree. apart 
from each other, into which the four bearing elements 19.sub.1 to 19.sub.4 
have their respective central legs 19a detachably fitted, so that the 
bearing elements surround the shaft. 
The wings of each of the bearing elements are of such a length that when 
the bearing elements are arranged about the shaft in the above-mentioned 
manner, the adjacent wings of the adjacent bearing elements partially 
overlap each other. The manner of overlapping of the adjacent foil wings 
depends upon the direction of rotation of the shaft 11. In FIG. 7, since 
the shaft 11 is rotated counterclockwise, the left-hand wing 19L of each 
bearing element 19 underlies or lies outside the right-hand wing 19R of 
the adjacent bearing element on the left-hand or clockwise side, while the 
right-hand wing 19R of the element overlies or lies inside the left-hand 
wing 19L of the adjacent bearing element on the right-hand or 
counterclockwise side. The length of the overlapping portions of the 
adjacent wings is determined in consideration of the size and position of 
the supporting elements to be described below. 
To impose a preload on the shaft, there are provided four resilient 
supporting elements 20.sub.1 to 20.sub.4 which are of T-shaped cross 
section similar to but smaller than the bearing elements 19.sub.1 to 
19.sub.4 and comprise a central leg 20a and a pair of wings 20R and 20L 
made of resilient foil and extending from the leg 20a laterally in the 
opposite directions and being slightly upwardly curved. 
In the interior surface of the bearing housing 13 there are provided four 
more slots or channels 16.sub.1 ' to 16.sub.4 ' spaced 90.degree. apart 
from each other and 45.degree. apart from the previously mentioned 
channels 16.sub.1 to 16.sub.4 for the bearing elements 19.sub.1 to 
19.sub.4. 
The supporting elements 20.sub.1 to 20.sub.4 have their respective central 
legs 20a fitted into the channels 16.sub.1 ' to 16.sub.4 ' so that the 
foil wings of the supporting elements 20 resiliently support the 
overlapping portions of the foil wings of the adjacent bearing elements 19 
thereby to cause a predetermined preload to be imposed on the shaft 11. 
The magnitude of preload on the shaft, that is, the pressure with which the 
foil wings of the bearing elements 19 contact the shaft depends upon the 
resiliency of the foil wings of the supporting elements 20 and can be 
adjusted or changed by changing the number of the bearing elements 
provided or by changing the size, shape and/or material of the foil wings 
of the supporting elements. 
As the shaft 11 is rotated at a speed higher than a predetermined speed, a 
dynamic pressure generated in the wedge-shaped spaces between the shaft 
and the bearing elements provides a fluid bearing effect for the shaft in 
a manner similar to that in the previous embodiments. 
In the embodiments of FIGS. 7 to 9, although the opposite foil wings of the 
bearing elements are of a different length, they may be of the same 
length. Although the leg and the wings are of the same material and formed 
as an integral body, the wings may be different parts which may be 
combined with the leg into a single body by means of welding. 
Each of the supporting elements may be divided along the width thereof or 
along the axis of the shaft into a plurality of component parts of the 
same T-shaped cross section. 
The arrangement of FIGS. 7 to 9 enables easy adjustment of the preload on 
the shaft and improves the performance of the bearing and makes the 
bearing suitable for high speed operation. Since considerable tolerances 
are allowed in the design and dimension of the foils, the bearing is 
suitable for mass production.