Bearing arrangement

A bearing arrangement which is to be used for supporting a rotatable shaft used in a system employing a pressurized medium at a pressure which is partially dependent on the speed of rotation of the shaft includes a main bearing sleeve mounted on a support and surrounding the shaft. The working medium is supplied between the shaft and the bearing sleeve to fully support the shaft in the bearing sleeve when the pressure of the working medium exceeds a predetermined value. The bearing arrangement further includes at least one, but possibly more than one, auxiliary bearing including a split bearing ring which has a conical outer circumferential surface and a stationary outer bearing ring surrounding the split bearing ring and having a conical inner ramp surface. A resilient spring acts on the split bearing ring in one axial direction of the shaft against pressure forces of working medium to cause the contact surface to slide on the ramp surface with an attendent reduction in the transverse dimensions of the split bearing ring to bring the inner surface of the split bearing ring into supporting contact with the shaft for the auxiliary bearing to furnish at least a portion of the required supporting effect when the pressure of the working medium is below the predetermined value.

TECHNICAL FIELD 
The present invention relates generally to bearings, and more particularly 
to a bearing for use in a system employing a pressurized working medium at 
a pressure which is related to the speed of rotation of the shaft that is 
supported by the bearing. 
BACKGROUND ART 
There are already known various constructions of bearings, among them such 
in which a pressurized fluid is being supplied into the bearing to form a 
thin supporting film which supports the shaft which is received in the 
bearing for rotation. Such bearings perform to satisfaction so long as the 
supply of the pressurized fluid is assured regardless of the rotation of 
the shaft, that is, so long as the thin supporting film is in existence at 
any time at which the shaft rotates, including the start-up and wind-down 
phases of the rotation of the shaft. On the other hand, the operation of 
such bearings leaves much to be desired when they are being used in 
applications in which the pressure of the pressurized fluid supplied to 
the bearing is dependent on the speed of rotation of the shaft that is 
rotatably supported in the bearing, since then the shaft may run "dry" 
during certain time periods, such as during the start-up and wind-down 
phases of rotation of the shaft when the pressure of the pressurized fluid 
is directly proportional to the speed of rotation of the shaft. This, of 
course, is very disadvantageous, since such "dry" operation results in an 
excessive wear of the bearing. Moreover, the bearing offers an excessive 
frictional resistance to the rotation of the shaft during such "dry" 
operation, which is especially disadvantageous during the start-up phase, 
since either the period of time needed to reach the required shaft speed 
is undesirably long, or the motor driving the shaft will have to be 
overdimensioned. 
Accordingly, it is a general object of the present invention to avoid the 
disadvantages of the prior art. 
More particularly, it is an object of the present invention to provide a 
bearing arrangement of the type here under consideration, in which the 
wear of the bearing material is reduced to a minimum. 
Yet another object of the present invention is to design the bearing 
arrangement of the above type in such a manner as to keep the 
frisupporting a rotatable shaft used in a system employing a pressurized 
medium at a pressure which is dependent on the speed of rotation of the 
shaft, this bearing arrangement including main bearing means that includes 
a bearing sleeve mounted on a support and surrounding a first portion of 
the shaft, and means for supplying the pressurized working medium between 
the first portion of the shaft and the bearing sleeve to fully support the 
shaft in the bearing sleeve when the pressure of the pressurized working 
medium exceeds a predetermined value. The bearing arrangement further 
includes auxiliary bearing means including at least one bearing member 
which is mounted on the support for displacement into and out of contact 
with a second portion of the shaft, and means for urging the bearing 
member into contact with the second portion of the shaft to furnish at 
least a portion of the required supporting effect when the pressure of the 
pressurized working medium is below the predetermined value. 
It is particularly advantageous when the bearing member is constituted by a 
split bearing ring which has a conical outer circumferential surface and 
when there is further provided an outer bearing ring which is stationary 
and surrounds the split bearing ring, this outer bearing ring having a 
conical inner ramp surface which is adapted to contact the conical outer 
circumferential surface of the split ring to act as a guide therefor. 
Then, the urging means advantageously includes resilient spring means 
which acts on the split bearing ring in one axial direction of the shaft 
to cause the outer circumferential surface of the split bearing ring to 
slide on the inner ramp surface of the outer bearing ring in the sense of 
reducing the transverse dimensions of the split bearing ring and bringing 
the inner surface of the split bearing ring into supporting contact with 
the second portion of the shaft. The pressure of the pressurized working 
medium may then advantageously be used to counteract the influence of the 
resilient spring means on the split bearing sleeve and to displace the 
split bearing ring in the opposite axial direction and out of contact with 
the second portion of the shaft when the pressure of the pressurized 
working medium exceeds the predetermined value. 
A particular advantage of the bearing arrangement according to the present 
invention is that the auxiliary bearing means acts as the exclusive 
bearing means at the commencement of the rotation of the shaft when the 
pressure of the pressurized working medium is at zero gauge, while the 
main bearing means and particularly the pressurized working medium 
supplied thereto acts as the sole bearing means during operation within 
the normal range of speeds of rotation of the shaft. This advantage is 
achieved because the auxiliary bearing means, which is advantageously made 
of a low-friction material, such as polyimide, filled polyimide or filled 
polytetrafluoroethylene, offers very low frictional resistance to the 
rotation of the shaft when active, while its supporting action protects 
the main bearing means which at that time is not protected by the film of 
the working medium since the latter is at an insufficient or non-existent 
superatmospheric pressure. On the other hand, only the still lower 
frictional resistance of the film of the pressurized working medium 
present in the main bearing means to the rotation of the shaft is 
effective during the normal operation of the equipment including the shaft 
when the pressure of the working medium as determined by the speed of 
rotation of the shaft exceeds the predetermined value, since then the 
auxiliary bearing means is out of contact with the second portion of the 
shaft. Thus, the bearing arrangement of the present invention takes 
advantage of the benefits of both self-lubricating bearings and working 
fluid lubricated bearings, without incurring the disadvantages of either 
one of them.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawing in detail, and first to FIG. 1 thereof, it may 
be seen that the reference numeral 1 has been used therein to identify the 
bearing arrangement of the present invention in its entirety. The bearing 
arrangement 1 is being used for supporting a shaft 2 for rotation about 
its longitudinal axis. The illustrated bearing arrangement 1 incIudes as 
one of its main components a housing 3 which acts as a main support of the 
bearing. The housing 3 is, in turn, supported, in any manner which is 
conventional and hence has not been illustrated, on another support of the 
equipment in which the bearing arrangement 1 is being used, be it a 
machine frame, a mounting element or portion, or an adjacent component of 
the equipment. To give an example, if the bearing arrangement 1 is to be 
used in an air conditioning or refrigerating system including a compressor 
or a pump for a refrigerant, the housing 3 may be secured to the 
compressor or pump housing or may be constituted by a portion of such 
compressor or pump housing. 
In any event, the system employing the bearing arrangement 1 utilizes a 
pressurized working medium, such as the aforementioned refrigerant or 
another fluid which is capable of being used as a lubricant in the bearing 
arrangement 1 as well and the pressure of which is dependent on the speed 
of rotation of the shaft 2. Thus, in the above example, the pressure of 
the refrigerant may be directly proportional to the speed of rotation of 
the shaft 2, even though not necessarily linearly and over the entire 
speed range of the shaft 2, for instance because the shaft 2 is being used 
to drive the compressor or pump. The bearing arrangement 1 is particularly 
well suited for use in situations where the working medium is a gas or 
vapor that possibly, but not necessarily, contains some entrained atomized 
oil. 
The housing 3 bounds an internal passage 4 in which a longitudinal section 
of the shaft is accommodated with a radial spacing from the inner 
circumferential surface of the housing 3. The above-mentioned working 
medium is supplied into the passage 4 through an opening 5 provided in the 
housing 3 and, as shown, through a supply pipe 6 which is partially 
received in the opening 5 and is sealingly secured to the housing 3. In 
operation, only such amounts of the working medium as are needed to 
replenish the working medium leaving the passage 4 due to leakage will 
actually be supplied into the passage 4; yet, the pressure of the working 
medium present in the passage 4 will be dependent on the pressure of the 
working medium in the system, for instance at the output of the pump or 
compressor. 
A bearing sleeve 7 constituting main bearing means is received in the 
passage 4 at a radial spacing from the internal surface of the housing 3 
and around a first portion 8 of the shaft 2, forming a gap 9 with the 
external surface of the first portion 8 of the shaft 2. The size of the 
gap 9 is in reality very small, substantially corresponding to the 
thickness of a supporting layer or film of the working medium which is 
formed at normal operating speeds between the inner surface of the bearing 
sleeve 7 and the external surface of the first shaft portion 8 during the 
rotation of the shaft 2. The size of this gap 9 has been greatly 
exaggerated in the drawing for the sake of clarity. The bearing sleeve 7 
separates the gap 9 from a distribution chamber 10 which is radially 
delimited by the external surface of the bearing sleeve 7 and by the 
internal surface of the housing 3. The bearing sleeve 8 is provided with a 
plurality of perforations or holes 11 through which the working medium can 
flow from the distribution chamber 10 into the gap 9 to form the 
aforementioned supporting film in the gap 9 when the shaft 2 rotates at a 
speed in the normal operating range. On the other hand, when the pressure 
of the working medium is below a predetermined value, which implies 
rotation of the shaft at a speed below the normal operating range, the 
external surface of the shaft 2 would contact the inner surface of the 
bearing sleeve 7 if the latter were the only bearing means for the shaft 
2. 
To avoid this possibility and the attendant excessive wear of the bearing 
sleeve 9 and/or of the first shaft portion 8 and the attendant undesired 
excessive frictional resistance to the rotation of the shaft 2, there is 
further provided an auxiliary bearing means 12 which is also received in 
the passage 4 and surrounds a second portion 13 of the shaft 2. The 
auxiliary bearing means 12 axially delimits the distribution chamber 10 
and supports the bearing sleeve 7. It is currently preferred to provide 
one such auxiliary bearing means 12 at each axial side of the main bearing 
means constituted by the bearing sleeve 7, but it will be appreciated 
that, under certain circumstances, one such auxiliary bearing means would 
be sufficient. 
The illustrated auxiliary bearing means 12 includes an annular outer 
bearing member 14 which is stationary relative to the housing 3 at least 
in the axial direction, be it because it is connected to the housing 3 in 
any known manner, because it is constituted by an integral portion of the 
housing 3, because it is confined, because the pressure of the working 
medium in the distribution chamber 10 prevents it from axial displacement, 
or because it is connected to the bearing sleeve 7. It is currently 
preferred to connect the outer bearing member 14 to the bearing sleeve 7 
by outwardly swaging an end portion 15 of the bearing sleeve 7 to form an 
interference fit with the outer bearing member 14. The auxiliary bearing 
means 12 further includes an annular inner bearing member 16 which is 
situated inwardly of the outer bearing member 14. As shown, the inner 
bearing member 16 includes a body 17 which may be of a metallic material, 
and a layer 18 of a low-friction or self-lubricating synthetic plastic 
material which lines the inner bore of the body 17. Suitable materials for 
the layer 18 include polyimide, a mixture including a polymer resin and 
polytetrafluoroethylene and other known self-lubricating materials to the 
extent that they are compatible with the working medium. When using the 
above mixture, the polytetrafluoroethylene may be present in the mixture 
in the form of particles which are uniformly distributed in a matrix of 
the polymer resin and/or ceramic particles may be interspersed in the 
mixture. While it is sufficient to provide only the layer 18 of the 
self-lubricating material on the interior of the core 17, the inner 
bearing member 16 could also be made of the synthetic plastic material in 
its entirety, and the outer bearing member 14 could be made of the same or 
of a different synthetic plastic material as well. The inner surface of 
the inner bearing member 16 is shown to surround the external surface of 
the second shaft portion 13 with a spacing 19. 
The outer bearing member 14 has an inner surface 20 which converges in the 
direction indicated by the arrow A to constitute a ramp surface. The inner 
bearing member 16 has an outer surface 21 which also tapers in the 
direction of the arrow A to constitute a contact surface. It is currently 
contemplated to make the surfaces 20 and 21 frusto-conical, but they could 
also have other configurations, for instance frusto-pyramidal, if so 
desired. The angles of convergence of the surfaces 20 and 21 are the same, 
so that the surfaces 20 and 21 are in area contact with one another when 
pressed against one another, and the contact surface 21 of the inner 
bearing member 16 is capable of sliding along the ramp surface 20 of the 
outer bearing member 14 with attendant reduction in the transverse 
dimensions of the inner bearing member 16, as will be discussed below. 
The bearing arrangement 1 further includes a resilient spring element 22 
which is shown to be juxtaposed with the respective end face of the 
housing 3. This spring element 22 stationary relative to the housing 3 at 
least in the axial direction, either by being physically connected thereto 
by screws or other fastening elements, or by being confined between the 
aforementioned end face of the housing and a flange or a similar confining 
element, for instance, a pump or compressor housing. As shown particularly 
in FIG. 2 of the drawing, the spring element 22 of the illustrated bearing 
arrangement 1 includes a plurality of radially inwardly extending 
resilient fingers 23 and an annular interconnecting portion 24 which 
connects the resilient fingers 23 with one another to give the spring 
element 22 a unitary construction. FIG. 2 also shows that the inner 
bearing member 16 is provided with a split 25 which is shown to extend 
radially through the entire inner bearing member 16 and which also extends 
over the entire axial length of the inner bearing member 16 to enable the 
same to radially expand and to be radially contracted by application of 
radially inwardly acting forces thereon. In its relaxed condition, the 
inner bearing member 16 is expanded, so that the spacing 19 is 
considerable. 
Turning now back to FIG. 1 of the drawing, it may be seen that the 
interconnecting portion 24 of the spring element 22 may serve as an 
abutment for the outer bearing member 14 if the axial position of the 
latter is not assured in any other way. On the other hand, the resilient 
fingers 23 of the spring element 22 are in contact with the outer end face 
of the inner bearing member 16 and urge the same in the direction of the 
arrow A. 
Having so described the construction of the bearing arrangement 1 of the 
present invention, its operation will now be explained, still with 
reference to the drawing. First, it is to be mentioned that the various 
components of the bearing arrangement are shown therein in the positions 
which they assume during the normal operation of the system in which the 
bearing arrangement 1 is used, that is, when the shaft 2 rotates at a 
speed above a predetermined threshold value and the pressure of the 
working medium is above a predetermined value. 
Under these circumstances, the pressure of the working medium in the 
distribution chamber 10 and in the gap 9 is sufficient to form the 
aforementioned shaft-supporting film in the gap 9. At the same time, the 
working medium leaves the gap 9 through the respective end of the bearing 
sleeve 7 and its pressure acts on that axial end face of the inner bearing 
member 16 which is closer to the bearing sleeve 7, causing displacement of 
the inner bearing member 16 opposite to the direction of the arrow A. Now, 
since the natural or relaxed state of the inner bearing member 16 is its 
expanded state, and since the confining or inwardly pressing action of the 
outer bearing member 14 on the inner bearing member 16 is reduced or 
eliminated altogether during this axial displacement of the inner bearing 
member 16, the latter expands substantially uniformly in all radial 
directions, thus creating the spacing 19. Thus, it may be seen that the 
bearing sleeve 7 and the working medium film formed between the same and 
the external surface of the first shaft portion 8 is the sole bearing 
means for the shaft 2 under these normal operating conditions. 
During the displacement of the inner bearing member 16 opposite to the 
direction of the arrow A, the resilient fingers 23 of the spring element 
22 are resiliently deflected by the action of the inner bearing member 16 
thereon, until an equilibrium is achieved between the spring forces 
exerted thereby and the pressure forces applied by the pressurized working 
medium on the inner bearing sleeve 16. Now, if the pressure of the working 
medium is reduced, the forces exerted by the resilient fingers 23 on the 
inner bearing sleeve 16 will outweigh the working medium pressure forces 
and displace the inner bearing sleeve 16 in the direction of the arrow A, 
so that the contact surface 21 of the inner bearing member 16 rides on the 
ramp surface 20 of the outer bearing member 14, resulting in radially 
inward deformation or contraction of the inner bearing member 16 and 
attendant reduction in the magnitude of the spacing 19, until the latter 
is eliminated altogether once the pressure of the working medium is 
reduced to the predetermined value. From then on, further reduction in the 
pressure of the working medium will result in further displacement of the 
inner bearing member 16 in the direction of the arrow A, causing the inner 
bearing member 16 to contribute more and more to the total supporting 
effort needed to support the shaft 2 by pressing more and more against the 
external surface of the second shaft portion 13, until finally the 
auxiliary bearing means 12 becomes the sole bearing means for the shaft 2 
when the gauge pressure of the working medium drops to zero. Of course, 
when the pressure of the working medium starts to rise again, as it does 
during a start-up operation of the equipment using the bearing arrangement 
1, the above process is reversed, so that the auxiliary bearing means 12 
is the sole bearing means for the shaft 2 initially and its function is 
gradually taken over by the bearing sleeve 7 and the working medium film 
building up in the gap 9 as the pressure of the working medium increases. 
Thus, it may be seen that the main bearing means is in effect only when it 
works most efficiently, while the auxiliary bearing means 12 takes over 
the shaft-supporting function only during such operating conditions where 
the main bearing means would be subject to excessive wear and would exert 
excessive frictional forces on the shaft 2. It will be appreciated that 
the above-discussed cooperation of the main and auxiliary bearing means 
brings about results which are vastly superior to those achieved by either 
one of these bearing means alone. 
It should be understood that the invention is not limited to the particular 
embodiment shown and described herein, but that various changes and 
modifications may be made without departing from the spirit or scope of 
the concept as defined by the following claims.