FIELD OF THE INVENTION
The present invention generally relates to bearing supports for (SFD) Squeeze Film Damper along with mechanism for spring preloading and centering of journal bearing. More particularly, the invention relates to a device for supporting a squeeze film damper on elliptical spring and adjusting spring preloading and centering of journal bearing.
BACKGROUND OF THE INVENTION
In rotating machinery, the vibration energy produced by rotation of the shaft is dissipated to heat. In this process, vibration response like displacement of shaft or transmission of excitation force on the bearing housing is reduced. The mechanism by which the vibration energy is converted into heat energy is known as damping. In oil filled journal bearing, the maximum damping can be achieved has a limitation. High speed machines like turbine, compressor, and generators are designed with flexible rotors and require an additional damping other than the maximum damping achievable through the journal bearing. For an improved rotor dynamic stability of the machine, Squeeze Film Damper (SFD) bearing are used for providing additional damping.
During designing of rotating machine using journal bearing and flexible rotor, it is a normal practice to carry out rotor dynamic analysis of the rotor bearing system and ensure that design parameters like damping, stiffness, unbalance response, critical speed etc are within acceptable limits. However, in few cases,

mainly due to manufacturing/assembly deviations, the actual characteristics may deviate from performance predicted at the design stage or even from similar type of machines. In these cases, exceeding the critical speed of the rotor, bearing system becomes difficult due to inadequate damping available in the machine. Similarly, If critical speed of the machine is nearing the operating speed, the separation margin is reduced and vibration becomes high. These situations can be controlled by designing a suitable Squeeze Film Damper (SDF) bearing.
SFD consists of a non rotating journal and a stationary outer bearing, both of nearly identical radius. The journal is mounted on an oil filled annulus space, and is prevented from spinning along with the pin, squirrel cage or spring of the journal centering mechanism as well. The spring takes the static load of the rotor. In operation, as the journal moves due to dynamic forces acting on the spring, it undergoes a cyclic deflection and the lubrication oil is displaced to accommodate these motions. As a result of this squeezing in oil, hydrodynamic pressures exert fluid film force on the journal surface and provide additional damping and reduce the rotor amplitude of motion. Additionally it also helps to control on excitation force from getting transmitted to the bearing pedestal.
The amount of damping produced is a critical design consideration. If damping is too large, the SFD act as a rigid constraint o the rotor-bearing system with large forces transmitted to the supporting structure. If damping is too light, the damper is ineffective and likely to permit large amplitude of vibration. Moreover, adequate damping contribution to rotor dynamic stability at high speeds by suppressing sub-synchronous of rotor natural frequencies.

SFD damper without entering spring mechanism is known in the art. These types of dampers are used in air craft engines, gas turbines, lightweight compressor rotors and auto-motive turbo-chargers. The outer race of the bearing is allowed to float between the bearing outer diameter and housing inner diameter. Th.s design is adopted mainly to address the difficulty in implementation of conventional spring based SFD due to space constraints.
The absence of spring in this type of design means that the damper journal bearing rests at the bottom during start up. As the rotor starts to rotate and speed increases, the dampers bearing shell outer surface is lifted. The oil in this design does not produce direct stiffness like conventional fluid film bearings. But the SFD develops direct stiffness like behaviour which is due to cross-coupled damping co-efficient of the oil film. These types of dampers are one of the most non linear in nature for two reasons. The first reason for non-linear behaviour is produced by cross coupled damping coefficients. The second reason for non linearly comes as a direct consequence of the bottoming out of the damper journal.
According to a known method, a centering spring provided in a squeeze film damper is the form of O-rings. Most commonly used material is elastomer. The main advantages of this type of SFD are its design simplicity and ease of manufacturing. Moreover, it requires low radial space which makes it a preferred method to retrofit with existing machine without any major changes in bearing housing. Use of such O-rings also helps in increase the overall damping effect by reducing the side leakage. A major disadvantage with this SFD design is the

limited range of stiffness that can be achieved with elastomers . Prediction of CD-ring stiffness is difficult in elastomeric materials due to the material variance, influence of temperature and wear on its properties. The O-rings design is also susceptible to creep, causing the damper to bottom out, which lead to a non¬linear spring behaviour. O-ring type dampers are not capable to withstand thrust load which makes them suitable for use with lightweight rotors only.
Squirrel cage supported dampers are one of the most commonly used SFD design in rotating machines like air craft, gas turbines etc. The squirrel cage dampers are relatively less nonlinear as compared to other two cases described above. Moreover the stiffness characteristics could be modeled to predict the damper behaviour at design stage.
The squirrel cage while designed as centering spring for the damper, requires thee to four times axial space as compared to damper itself. This high axial space requirement is one of the major drawbacks of this design.
Assembly methodology of squirrel cage spring and centering the journal within the available clearance space requires special skills and tools. The spring of the squirrel cage complicates the design of damper end sealing and its assembly. It is also difficult to offset the spring assembly while it is under static load of the rotor. Maintaining the parallelism of accurate centering between the damper journals and bearing housing are another challenge for this type of SFD design.

Recently developed integral SFD design, addresses the issue of axial space constraints effectively. Use of WEDM technique allows manufacturing of journal bearing, outer race and spring as an integrated component. This design results in compact, cost effective and ready to use solution which does not require major change in existing bearing pedestal. However, it requires a special type of material because the spring itself undergoes cyclic deflections due to dynamic loading of the rotor and experiences the stress. Design of squeeze film damper annular space is critical parameter for optimal performance of the bearing. Spring stiffness and dynamic load variation are to be considered to decide this annular space. Typically the radial gap requirement is 50. Use of WEDM process means the spring profile is to be cut along the entire length of the SFD which reduces total effective damping area. The residual stresses resulting from the WEDM process can cause dislocation of the structure relative to the case. In order to avoid excessive warping, it is necessary to provide a relaxation period for the stresses to subside before the bore profile is given a final cut. This results in a additional manufacturing step where the outside diameter of damper is machined or ground concentric to the inside diameter.
Inspection of the integral centering spring is difficult due to the one-piece construction and very narrow annulus space availability. On the other hand for maintenance purpose, it is often difficult to clean the narrow oil passages due to the limited access. Repair of this dampers are also quite difficult.
Air foil bearings and gas lubricated deflecting pad bearings are also used to provide additional damping to rotating machinery like air cycle machine on air craft (ACM) or gas turbines. Bu its usage is limited to lightweight rotors and machines.

Some of the Patents related to SFD bearings are given below:
1. The Patent No. US 371169 published on January 16,1973
2. The Patent No. US 4025130 published in September 27,1983
3. The Patent No. US 4553855 published in November 19,1985
4. The Patent No. EP 2187072A1 published in May 19, 2010
5. The Patent No. US 8083413B2 published in December 27, 2011
6. The Patent No. EP 2187072B1 published in September 12, 2012
7. The Patent No. 2014/0353102A published in December 4, 2014
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose device for supporting a squeeze film damper on elliptical spring and adjusting spring preloading and centering of journal bearing.
SUMMARY OF THE INVENTION
In this invention a SFD is designed that can be used in rotating machinery to provide damping with additional features. The essential features of the embodiments are adapting an elliptical spring, inbuilt provision for centering of the SFD journal inside the housing, and control the preloading of the spring, ease of manufacturing, improved provision for component inspection and maintenance. In order to accommodate heavy rotors, proposed SFD can be used with springs of different thickness combinations at the bottom and top

locations of the SFD. Moreover, the springs can be easily changed. Present invention is cost effective, because spring material used is although a special typed, but all other parts are made of regular material. Moreover, after its operating life or in case of damage of the springs, it can be replaced easily, at a minimum cost. A special type elliptical spring is designed for this SFD and it is manufactured using WEDM process.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: shows SFD bearing configuration without side cover plates, spring preloading and journal centering mechanism, bearing housing details of the invention is explained.
Figure 1A: Front view of figure 1, showing the top and bottom part of the bearing housing, its fixing mechanism, orientation of spring preloading bolts.
Figure IB: Cut away view of Figure 1A along the line A-A illustrating an overall assembly sequence of bearing journal, SFD Shell, SFD Shell Support, Elliptical spring support location and its mechanism.
Figure 2: Isometric view of Elliptical Spring which shows shape and locating hole position.
Figure 3: Isometric view of spring preloading and Journal Bearing centering bolt, and Lock nut.

Figure 4A: Isometric view of Journal Bearing Bottom Half, including its spring locations and babbit surface.
Figure 4B: Isometric view of Journal Bearing Top Half, including its spring locations and babbit surface, fixing position of Journal two halves and its locating pin holes.
Figure 5A: Isometric view of SFD Shell Bottom Half, including its shape, oil groove details, locating pin positions and spring assembling pockets.
Figure 5B: Isometric view of SFD Shell Top Half, including its shape, oil groove details, locating pin positions and spring assembling pockets.
Figure 6A: Isometric view of SFD Shell Support Bottom Half and details and features of the Bottom Shell support.
Figure 6B: Isometric view of SFD Shell Support Top Half including details and features of the Bottom Shell support.
Figure 7A: Isometric view of Bush shows it shape and details.
Figure 7B: Cut away view of Figure 7A along the line B-B, depicting internals section of bush, 0-ring location, threaded and unthreaded portions of the bush and its fixing locations.

Figure 8A: Isometric view of side cover plate.
Figure 8B: Cut away view of figure 8A along the line C-C that shows the cross section of the cover plate and its fixing positions.
DETAILED DESCRIPTION OF THE INVENTION
While reading the drawings and elements it is to be noted that the identical numerals used in different drawings and views denote same elements. Figure 1 to 8B is detailed here to explain the present invention.
Figure 1 shows the Journal Bearing Top 18 and Journal Bearing Bottom Half assembly 19 which forms the core of the SFD, its internal cylindrical babbit surface makes the passage for rotating shaft to pass through. Element 18 and 19 forms normal oil filled journal bearing. Outside surface of Journal element 18 and 19 are cylindrical and they are assembled inside a SFD Shell having Bottom element 11 and Top element 8 respectively. Similarly SFD shell is assembled inside SFD Shell Support elements 2 and 4. Journal is supported inside SFD shell using elliptical springs 7. A clearance passage element 52 between Journal and SFD Shell is filed with oil. During operation, spring element 7 undergoes deflection and allows oil to get squeezed in the passage 52. Springs are assembled within rectangular pocket 9. Four numbers of springs are used on each side of the SFD at 90 degree angular spacing. Springs are assembled in such a manner that its landing 30 are on internal surface of bearing journal pocket and hole location 29 is towards SFD Shell (refer Figure 1 and 2 ). A central hole 29 is designed on the elliptical spring element 7 such that a long bolt

32 with its tip of lower diameter 33 is inserted (Refer Figure 1, 2 and 3). Bolt 34 is assembled from the surface of the bearing housing through hole elements 15, such that the springs arrest inside the SFD shell pockets 9, its preloading and centering of the journal in the core with respect o he rotating shaft is achieved. After assembly, uniformity in clearance of passage 52 is ensured using filler gauge measurement and after achieving desired clearance, adjustment bolt 34 is locked on the housing using locking nut 14 (Refer Figure 1 and Figure 3).
Static load of the rotor is carried by bottom springs and during dynamic loading all the springs undergo cyclic deflection and expansion and make oil to get squeezed in the passage 52 and thus provide additional damping to the rotor dynamic system.
Figure 1A shows the front view of Figure 1. It shows longer bolt 34 adjustment passage 15 and its configuration with respect to overall SFD.
Figure 1B shows cut way view of Figure 1A along line A-A. In this view top journal babbit element 20, bottom journal babbit 21 and journal top 18 and journal bottom 19 assemblies are shown. SFD Shell is assembled inside the bearing pedestal support bottom 2. Similarly journal top 18 is assembled inside SFD Shell top element 8. For better assembly accuracy of element 18 and 8 a provision for locating pin 25 is arranged. Shell top element 8 is assembled inside SFD bearing support pedestal top 4. The locating pin position 23 is used for proper assembly of element 8 and 4. The mating surface of SFD Shell and SFD Shell Support are spherical in nature which improves assembly stability during the operation of rotor.

Spring element 7 is shown in Figure 2. Special alloy steel is used and tested after manufacturing for stiffness characterization. It is designed in elliptical in shape with two side landings 30 for its proper sitting inside the rectangular pocket. In the centre of the spring hole 29 is made such that tip 33 of bolt 34 is inserted and could be tightened for proper preloading to the spring.
Shape of the adjustment bolt is shown in Figure 3. It has tip 33 and locking nut 34.
Journal bearing bottom half element 19 is shown in Figure 4A. It has provision for elliptical spring sitting 31, oil entry path 32 and babbit surface 21.
journal bearing half element 18 is shown in Figure 4B. It has provision for elliptical spring sitting 36, oil entry path 35 and babbit surface 20, top and bottom half bolting provision 37 and journal bearing assembly pin locating hole 35.
Centre of the SFD Shell is designed with grooves 39 at top and 24 at bottom. It ensures oil supply to the journal and SFD damper. Hole element 3 on both sides of the bearing pedestal 2 are the oil supply points to the SFD. Supplied oil fills up bottom groove 24 and then subsequently groove 39 is filled up. Bearing support pedestal top and bottom element 2 and 4 are assembled though the counter-shunk bolts utilizing the passage similar to 16 (refer Figure 1A). Flow of oil within the two chambers of element 1 allowed using cut way passage 17 (refer Figure 1B). Similarly oil drainage from the element 1 is commenced using hole element 6 (Refer Figure 1).
Figure 5A shows shape of bearing shell bottom 11, oil groove 24, adjusting bolt passage hole 40 and fixing pin location 41. Oil to groove 24 is supplied through

hole 38 and is in line with hole 3 of Figure 6A. There are two rectangular pockets on each side for assembly of elliptical spring element 7.
SFD shell top half 8 is shown in Figure 58. Oil groove element 39 and top and bottom shell bolt assembly location 42. Two halves of the SFD shells are assembled using location 42 for bolt insertion.
SFD shell support bottom 2 is shown in Figure 6A. It shows top and bottom shell support positioning pin location 43, oil flow passage 44, adjusting bolt insertion hole 45 and oil inlet hole 46. Bottom part of the SFD shell element 11 is assembled inside element 2.
SFD shell support top element 4 is shown in Figure 6B. Top half of the SFD Shell element 8 is assembled inside 4. Relative motion of the SFD Shell and SFD Shell supports are restricted using locating pin at position 48. Adjustable bolt 34 insertion passage is location 49.
Bush isometric and cut way views are shown in Figure 7A and 7B. Bush is assembled to the shell support (bearing housing) using bolts location similar to 26. Core of the bush 5 is hollow 28 that has both threaded and unthreaded portions. At the core of bush o-ring insertion position 27 is provided. Bush 5 element is used for bolt 34 tightening without any oil leakage during operation.
Figure 8A and 8B shows isometric view and cross section of side cover plate 10 (refer Figure 1B). It is assembled on the bearing housing using the fixing bolt location similar to 51. Side cover plates are used to stop splashing of oil from the rotor during its operation.

WE CLAIM :
1. A device for supporting a squeeze film damper on elliptical spring and adjusting spring preloading and centering of journal bearing, the squeeze Film Damper (SFD) comprising a shell having a bottom element (11) and a top element (8), the shell being assembled inside support elements (2,4), the device comprising :
- a journal bearing assembly having a top half (18) and a bottom half (19), each having cylindrical outer surface and an internal babbit surface (20, 21), the babbit surfaces (20, 21) forming a passage for rotating;
the journal bearing assembly (11, 8) attached to the support elements (2,4) inside the SFD shell and supported by a plurality of spring (7) disposed in a rectangular pocket (9);
a clearance passage (52) provided between the journal bearing assembly and the SFD shell filled with oil;
wherein the springs (7) upon application of dynamic loading of the rotor undergo cyclic deflection including expansion to cause the oil squeezed inside the passage (52) ad provide additional damping to the rotor system.
2. The device as claimed in claim 1, wherein each of the springs (7) comprises a central hole (29) and a landing (3), and wherein four springs (7) are provided on each side of the SFD shell at 90° angular spacing.

3. The device as claimed in claim 1, comprising a bolt (34) arranged inside the central hole of the spring (7) extending through hole elements (15) of the bearing housing such that the springs (7) during operation get arrested inside the SFD shell pockets (9) and wherein the preloading and centering of the journal is achieved.
4. The device as claimed in claim 1, wherein he spring is constructed in elliptical shape using alloy steel with stiffness characterization, and wherein the central hole (29) on the spring (7) is made to allow a tip (33) of said bolt (34) to be inserted and tightened for pre-loading of the spring (7).