Spring supported damping system

A damper system for supporting a bearing for a rotating shaft of a gas turbine engine includes a plurality of cylinders circumferentially spaced about the outer race of the bearing with a reciprocating piston in each of the cylinders having one face bearing against the outer race and the other face disposed in a fluid-filled chamber with an inlet and restricted outlet that forces the liquid in and out of the chamber in response to the vibratory motion as the outer race orbits about the cylinders exciting the piston to effectuate a pumping action.

CROSS REFERENCE 
The subject matter of this application is related to the subject matter of 
commonly assigned U.S. patent application Ser. No. 07/560,985 filed on 
even date herewith and entitled "Dashpot Damper". 
FIELD OF THE INVENTION 
This invention relates to dampers for bearings supporting a rotating shaft 
of rotating machinery and more particularly to dashpot dampers for 
bearings supporting the shaft of the compressor/turbine rotor of a gas 
turbine engine. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 4,213,661 granted to R. A. Marmol on July 22, 1980 and 
entitled "Bearing Support Structure Combining Fluid Damping and Spring 
Damping Apparatus" assigned to United Technologies Corporation, the 
assignee common to this patent application discloses a fluid damper and 
arcuate spring damper combination. In the structure disclosed in the 
patent, supra, seals isolate the ends of the fluid filled damping chamber 
to form a tight compartment for the oil to effectuate damping. U.S. patent 
application Ser. No. 07/417,108 filed on Oct. 4, 1989 by R. Carlson and 
entitled "Fluid Damper And Spring" similarly assigned to United 
Technologies Corporation discloses a spring that is fabricated from 
arcuate segments that when assembled surround the bearing and include a 
plurality of circumferentially spaced oil filled chambers entrapped by a 
"race track" shaped "O" ring seal also effectuating damping. While these 
systems, just described above, provide efficacious damping, they 
nonetheless present certain problems. As for example, the curved beam 
springs are manufactured to extremely close tolerances which is expensive 
and are difficult to assemble. In addition, these components are highly 
stressed and are subjected to wear which are at magnitudes that in certain 
installations may be intolerable. The "race track" shaped groove for the 
"O" ring seal is prone to seal blowout. Under adverse circumstances or 
poor assembly practices the seal can become extruded from the groove and 
get pinched between the beam and its housing with a consequential 
destruction of the seal and a subsequent loss of oil and its attendant 
damping capability. 
I have found that I can obviate the problems noted hereinabove by providing 
a dashpot damper system that is judiciously mounted around the outer race 
of the bearing supporting the rotor shaft of the gas turbine engine. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide an improved damping and spring 
support system for the rotor of rotating machinery. 
A feature of this invention is to provide for a gas turbine engine a 
plurality of circumferentially spaced dashpots each of which includes a 
piston surface that bears against the outer surface of the outer race of 
the bearing supporting the rotor shaft which is characterized as being 
simple to manufacture, relatively inexpensive, is flexible in design as to 
preloads, spring rate, spring response, seal types, contact area and 
damping volume. Additionally, the seal for the fluid-tight cavity of the 
dashpot is ideally located inasmuch as it avoids the extrusion problem 
alluded to hereinabove.

BEST MODE OF CARRYING OUT THE INVENTION 
While in its preferred embodiment, the invention is contemplated to be 
utilized on a radial bearing for gas turbine engines, it will be 
understood that the invention can also be employed with other types of 
bearings and for any rotating machinery where it is desired to minimize 
the effect of adverse vibrating motion. For additional details relative to 
damping systems used in gas turbine engines reference should be made to 
the U.S. Pat. No. 4,213,661, supra. 
As best seen in FIGS. 1 and 2, the invention in its preferred embodiment is 
shown with a bearing support system for a rotating shaft that consists of 
the shaft 10 and roller bearing 11 having an inner race 12, an outer race 
14 and a plurality of circumferentially spaced rollers 16 sandwiched 
between outer race 14 and inner race 12. Cage 18 serves to provide the 
spacing between rollers. The bearing is supported to the bearing housinq 
generally indicated by reference numeral 20 as shown in schematic fashion. 
What has been just described is a typical radial bearing used in gas 
turbine engines. In accordance with this invention, a plurality of equally 
spaced cylindrically shaped chambers 22 formed in housing 20 circumscribe 
the bearing and each chamber carries a reciprocating piston 24 slideably 
mounted in each chamber 22. The outer face 26 of piston 24 bears against 
the outer surface of outer race 14. 
As is apparent, from the foregoing, piston 24 essentially divides chamber 
22 into two portions, the portion being occupied by piston 24 and the 
other portion facing the inner face 30 of piston 24 and together with the 
cylinder wall define sub-chamber 32. A suitable seal 34 which may take the 
form of an elastomeric "O" ring, "U" ring, metal piston ring or the like, 
fits into a groove that circumscribes the piston 24 and prevents leakage 
between piston 24 and the cylinder wall. 
The end of sub-chamber 32 is blocked off by plug 34 suitably threaded into 
the threads formed in the wall of cylinder in housing 20 adjacent the 
outer end. A suitable spring 36, preferably a Belleville washer type, 
disposed between the end of plug 34 and face 26 of piston 24 provides a 
spring force that centers bearing 11 and keeps the piston 24 in contact 
with the outer race. Obviously, adjusting the height of plug 34 by 
screwing it in and out of the cylinder varies the spring compression and 
consequently changes the spring force. The plug can be locked in the 
desired position at a prerequisite preload by a suitable nut 40 and washer 
42 or such similar means. 
As would be apparent to one ordinarily skilled in this art, the preload can 
be obtained by other means, such as by utilizing different classes of 
springs, different thickness, heights and the like. 
As noted in FIGS. 3 and 4, this invention comtemplates utilizing a fixed 
opening for receiving the spring and hence preselects the spring rate. For 
example, in FIG. 3, plug 34, pre-formed with shoulder 49 seats against the 
complimentary shoulder 51 formed in housing 20 when assembled. (Like 
reference numerals reference like parts in all the FIGS.) 
In FIG. 4 housing 20 is configured so that the outer end of the cylinder is 
closed which, like the embodiment in FIG. 3 pre-ascertains the dimension 
of the spring. 
Fluid, such as damping oil, is supplied under pressure from a source (not 
shown) to annular manifold 42 formed in housing 20 via passageway 44 and 
is admitted to sub-chamber 32 through drilled holes 46. This piston 24 
reacting to the orbiting motion of the outer race 14 which is excited by 
the vibrating energy caused by the rotating shaft, behaves as a pump and 
forces the oil out of sub-chamber through the drilled restrictive 
passageway 50, communicating with manifold 48. This oil in manifold 48 is 
bled out of the damping system via drilled passageway 52. The oil being 
forced out of and into sub-chamber 32 dampens the vibrating energy. 
Slots 54 may be formed in the head of plug 34 and a skirt may be employed 
with piston 24 to enhance the flow of oil around spring 36. 
As is apparent from the foregoing, the squeezing of oil out of sub-chamber 
32 and the continuous supply of oil keeping the volume of sub-chamber 32 
completely filled effectuates damping in a similar manner as a dashpot 
damper. The bearing loads forcing the piston 24 outward is counteracted by 
the loads provided by the oil acting on the face 26 of piston 24 and the 
spring load provided by spring 36. 
The damping system can be optimized or tuned by the proper sizing of the 
inlet passages 44 which is larger than the restricted outlet passage 50 
and the use of check valves on the inlet and outlet oil circuit. 
The gap illustrated by reference letter A between the outer surfaces of 
outer race 14 and the inner diameter of housing 20 serves as a stop for 
the outer race and affords a simple solution to controlling the design of 
the outer race stops. 
FIGS. 4, 5 and 7 are exemplary of the types of pistons that can be employed 
with this invention. In FIG. 4 the face 60 of piston 24 is contoured to 
complement the contours of the outer surface of outer race 14. In FIG. 5 
the face 62 of piston 24 is dome shaped and contacts the outer race at the 
tangent of the respective arcs of the outer race and dome. And in FIG. 6 a 
protrusion 64 extends axially from the end of piston 24 and face 66 on 
protrusion 64 contacts outer race 14. 
What has been disclosed by this invention is a relatively simple, compact 
damping system that offers the following advantages and differences 
relative to a curved beam damper system as of the type disclosed in U.S. 
Pat. No. 4,213,661, supra, 
Utilization of Belleville springs allows for a more compact and less 
expensive design than achievable with curved beams. Furthermore, the 
Belleville spring allows for choice of linear, constant, or non-linear 
response by specifying a certain height to thickness ratio. 
Preload/centering force on the bearing is adjustable either by using the 
threaded plug design or by changing classes of springs. This provides a 
distinct advantage over curved beams both during development and when 
making changes. The tolerance stackup on curved beams causes a wide 
variation in preload while the dashpot damper preload can be selected and 
adjusted. changes to curved beams require a detailed analysis and redesign 
customized for each application. 
This invention accommodates more conventional machining techniques than 
curved beams. There are fewer critical dimensions and those that are 
required are easier to control. 
This invention provides a simple easy to control outer race stop at two 
locations. 
Contact area, oil volume, and oil are easily modified by altering the 
piston head shape, hollowing it, etc. Curved beams are difficult to modify 
since they are highly stressed structural members. 
This piston/cylinder system is inherently easier to seal than the curved 
beam designs since it uses circular seals around a piston rather than 
"race track" seals in beam as disclosed in the aforementioned U.S. patent 
application. 
The piston will act as an efficient pump as it moves in and out. Use of 
check valves and various passage designs will allow the system to be tuned 
for optimum oil flow and damping. 
The flexibility in the dashpot system as taught by this invention allows 
for adaptation for various bearing applications as contrasted with the 
curved beam design must be customized for each application. 
Although this invention has been shown and described with respect to 
detailed embodiments thereof, it will be understood by those skilled in 
the art that various changes in form and detail thereof may be made 
without departing from the spirit and scope of the claimed invention.