Claims
- 1. A rotary machine which includes a rotor shaft and support structure for the shaft, the rotor shaft being rotatable at a first speed and a second speed, which comprises:
- an adjacent support structure which is spaced radially from the shaft;
- a member disposed about the shaft which is adapted to rotatably support the rotor shaft and which is spaced from the adjacent support structure leaving a damping chamber that is circumferentially continuous and that is disposed circumferentially about the member for damping vibrations in the shaft therebetween;
- means for flexibly supporting the member from the adjacent support structure which permits vibrational movement of the shaft in response to rotation of shaft;
- means for disposing damping medium in said damping chamber at said first rotational speed of the rotor shaft to provide a viscous damper for damping vibrational movement of the rotor shaft, and for removing damping medium from said damping chamber at said second rotational speed of the shaft to remove the viscous damper from the rotary machine at said second speed.
- 2. The rotary machine of claim 1 wherein the rotary machine further includes a stator assembly and wherein the adjacent support structure is a portion of the stator assembly.
- 3. The rotary machine of claim 1 wherein the means for disposing and removing damping medium from the damping chamber includes means for flowing pressurized damping medium to the damping chamber at the first rotor speed and blocking the flow of damping medium to the damping chamber at the second rotor speed, and, further includes means for venting the damping chamber whereby vibrational motion of the shaft forces the damping medium from the damping chamber
- 4. The rotary machine of claim 3 wherein the means for flowing and blocking pressurized damping medium to the damping chamber includes a pump and a conduit between the pump and the damping chamber and further includes means responsive to rotor speed for interrupting flow through the conduit.
- 5. The rotary machine of claim 4 wherein the means for interrupting flow in the conduit is a valve.
Technical Field
This is a division of co-pending application Ser. No. 07/507,950 filed on Apr. 11, 1990 which is a divisional application of application Ser. No. 07/193,449, filed on May 12, 1988, now U.S. Pat. No. 4,947,639 issued Aug. 14, 1990.
This invention relates to a method and apparatus for supporting a rotating shaft in a rotary machine. More particularly, the invention relates to reducing vibrations in machine structure, such as in the rotating shaft or in the support structure for the rotating shaft. The invention was developed in the field of axial flow rotary machines, and in particular gas turbine engines, but has application to other fields where viscous damping is employed to reduce vibrations.
Rotary machines employing rotor shafts supported by a bearing from a support structure are commonly used in gas turbine engines During operation of these engines, the range of rotational speed of the rotor may vary from low speeds to high speeds of over ten thousand revolutions per minute.
As pointed out in U.S. Pat. No. 4,669,893 issued to Chalaire et al entitled "Annular Oil Damper Arrangement", small imbalances associated with the rotating shaft may cause the actual axis of the rotor shaft to cyclically orbit the ideal axis of the rotor shaft with a frequency equal to the angular speed of the shaft.
Such orbiting motion is commonly referred to as synchronous vibration or whirl of the shaft. The lateral or transverse vibration of the center line of the shaft away from the ideal center of rotation increases as the rotor speed of the shaft approaches the resonant frequency of the support system (critical speed) associated with one of the different modes of vibration of the shaft. The resonant frequency is a function of the stiffness of the support system.
Vibratory forces in the rotor shaft are transmitted from the rotor shaft through the support system to the engine and from the engine to its mounting structure. Because the displacement of the shaft from the ideal axis of rotation is believed to increase these forces, devices are often employed to decrease the actual displacement of the shaft from the ideal center line of the shaft.
As shown in U.S. Pat. No. 4,669,893 issued to Chalaire, one device for decreasing the displacement of the shaft and, therefore, the forces which are transmitted from the shaft to the engine and to its supporting structure is a viscous damper having a fluid damping film which is disposed between the rotor system and its support. As shown in Chalaire, the film is disposed between the bearing housing of the rotor and the adjacent structure. Other examples of such dampers are shown in: U.S. Pat. No. 4,337,983 issued to Hibner entitled "Viscous Damper"; U.S. Pat. No. 4,084,861 issued to Greenberg et al entitled "Thrust Bearing Damping Means"; and, U.S. Pat. No. 31,394 issued to Streifert entitled "Flexible Damped Bearing Assembly".
In several of these dampers, the support for the shaft includes a bearing and its housing. The bearing and housing are positioned by a spring which resists the movement of the shaft away from the ideal center line of the shaft. The damper through its fluid damps orbital motion of the shaft. Damping is especially critical if the shaft is rotated at a speed which is the natural resonant frequency of the support system. As mentioned earlier, the speed is commonly referred to as the critical speed of the support system and is a function of the stiffness of the support system.
U.S. Pat. No. 3,756,672 issued to Hibner et al entitled "Shaft Damping Arrangement" and U.S. Pat. No. 4,046,430 issued to Buono and Hibner et al entitled "Damped Intershaft Bearing and Stabilizer" show the use of viscous dampers of the type discussed above for damping vibrations in concentric shafts. In U.S. Pat. No. 4,046,430, one shaft of a pair of concentric shafts is the structure from which the positioning spring extends to the bearing housing. The shaft with the bearing housing bounds the viscous damper cavity. Thus, the support structure for the bearing is a rotating component of the engine. In this particular invention, the spring in parallel with the damper is used to change the resonant frequency of one of the shafts so that the critical speed of the other shaft is no longer in the operating range of the engine.
Another approach is to use both viscous and frictional damping to damp vibrations as is shown in U.S. Pat. No. 4,353,604 issued to Hibner et al entitled "Viscous/Friction Damper". As shown in this patent, the support system for a rotating shaft includes both a viscous damper and a friction damper which is in series with the viscous damper. The friction damper is activated when a large imbalance of the engine rotor takes place which exceeds loads normally handled by the viscous damper.
Viscous and frictional damping are shown in U.S. Pat. No. 4,213,661 issued to Marmol entitled "Bearing Support Structure Combining Fluid Damping and Spring Damping Apparatus". In this patent, a plurality of arcuate beams are disposed in the damping cavity to provide frictional damping to the bearing.
A viscous and frictional damper is also shown in U.S. Pat. No. 3,456,992 issued to Kulina entitled "Vibration Damping Device". In Kulina, the squeeze film damper uses piston ring seals which seal the damper cavity. The piston ring seals are used as frictional devices pressed by damping fluid pressure against the walls bounding the damping cavity to develop a frictional force. Because the frictional force is proportional to pressure in the cavity and because the pressure in the cavity affects the viscous and stiffness characteristics of the damping medium, it is possible to tune the damper so as to get maximum viscous and frictional damping of motion at the critical speed characteristic of the rotor shaft. This provides damping of vibrations at the critical speeds for the shaft.
The above art notwithstanding, scientists and engineers working under the direction of Applicant's assignee are seeking to develop other devices for effectively reducing vibrations from rotor whirl.
This invention is predicated in part on the recognition that the presence of the damping fluid in viscous dampers under certain operating conditions may increase vibration in a rotary machine such as in the rotor shaft or in the support structure for the shaft.
According to the present invention, a support system for a rotor shaft includes a viscous damper having a damping chamber through which fluid damping medium is flowed and a device for allowing the flow of damping medium t the damper chamber at a first rotor speed to activate the damper and for blocking the flow of damping medium to the chamber in response to a second rotor speed, to remove the damper from the support system.
In accordance with one embodiment of the present invention, the device permits flow to the fluid damper at speeds no greater than the idle speed for the engine and prevents flow of oil to the damper at speeds above the idle speed characteristic.
According to one embodiment of the present invention, a method of operating a rotary machine having a rotating shaft and a viscous damper for the shaft includes flowing fluid damping medium to the damper at certain preselected rotor speeds and not flowing at other speeds to remove the damper from the machine.
A primary feature of the present invention is a support system for a rotary machine having a viscous damper which is disposed between a rotor shaft and the adjacent structure from which the shaft is positioned. A spring extends from the adjacent support structure to position the shaft in the damper. The damper has a damping chamber and means for venting the chamber which allows fluid damping medium to escape from the chamber. In one embodiment, the means for venting are passages, either small connected passages such as exist between the seals of the damping cavity, or in another embodiment, the passage is a larger discrete passage, such as an outlet conduit. Another primary feature is a device for turning on or off the flow of damping medium to the damping chamber in combination with the drain passage. In one embodiment, a pump driven by the rotor shaft for pressurizing the fluid damping medium supplies the damping medium at a pressure which is indicative of the speed of the rotor shaft. The device for turning on or off the flow of damping medium to the chamber is a check valve sensitive to the pressure of the damping medium. In one of these embodiments, the device for turning on or off the flow includes a pair of check valves in parallel, one permitting flow below a certain pressure (thereby turning off flow above a preselected first rotor speed) and the other permitting flow above a certain pressure (thereby turning on flow at a second rotor speed which is greater than the first rotor speed). In an alternate embodiment, the on-off flow device is an on-off solenoid valve responsive to a rotor speed signal.
Another feature of the present invention is a support system for the rotor shaft having a first stiffness characteristic (and an associated first critical speed characteristic) which results from flowing damping medium to the damping chamber and filling the damping chamber with the fluid damping medium; and, a second stiffness characteristic (having a second critical speed characteristic) which results from not flowing damping fluid medium to the damping chamber such that the fluid damping medium has no hydrodynamic stiffness. In one detailed embodiment, the method includes activating the damper at the first critical speed characteristic to damp vibrations of the rotary machine and removing the damper from the support system at a higher rotor speed to avoid the second critical speed characteristic of the support system. In an alternate embodiment, the method is to activate or inactivate the damper to operate all rotor speeds away from critical speed characteristic of the system.
A primary advantage of the present invention is the fatigue life of components which results from reducing the level of vibrations in a rotary machine by employing a viscous damper over a specific speed range and removing the damper from the system over another speed range. Another advantage is the reduction in vibrations and noise transmitted from the exterior of the machine to adjacent structure which results from reducing vibrations in the machine. In one embodiment, an advantage is a rotary machine which avoids and never operates at a critical speed characteristics by selectively changing the system stiffness through turning on and off the viscous damper to change the critical speed characteristics of the engine as a function of rotor speed. In one embodiment, an advantage is the simplicity of operation which results from the automatic removal of the damper from the system by using a pressure sensitive check valve and a fluid damping medium having a pressure which is indicative of rotor speed.
The foregoing features and advantages of the present invention will become more apparent in light of the following detailed description of the best mode for carrying out the invention and the accompanying drawing.
US Referenced Citations (2)
| Number |
Name |
Date |
Kind |
|
4775248 |
Barbic et al. |
Oct 1988 |
|
|
4782919 |
Chalaire et al. |
Nov 1988 |
|
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 0152951 |
Sep 1983 |
JPX |
Non-Patent Literature Citations (1)
| Entry |
| Adams, "Keep Rotor Vibration Under Control", August/1978. |
Divisions (2)
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Number |
Date |
Country |
| Parent |
507950 |
Apr 1990 |
|
| Parent |
193449 |
May 1988 |
|
Patent Grant
5110257
