Mass impact damper for rotors

Abstract: A vibration damper (24) of a rotating shaft (10) includes a floating housing (26) attached to the shaft (10) for radial vibratory displacement as a unit therewith, a plurality of cylindrical bores (42) in the floating housing (26) parallel to the axis of rotation (16) of the shaft (10), and a plurality of smaller cylindrical impactors (46), each one of which is movably retained within a respective bore (42). Each impactor (46) comprises a metal sleeve (50) containing a smaller cylindrical tungsten rod (54) movably retained therein, with a damping medium (56) around the rod (54). When the shaft (10) experiences radial vibratory displacement, each sleeve (50) impacts the wall of the respective bore (42), causing the damping medium (56) to be squeezed from between the tungsten rod (54) and the respective sleeve (50) for vibration damping energy absorption in one mode. In addition, the tungsten rods (54) impact the respective bores (42) through the sleeves (50) and initiate local plastic deformation of the bores (42), the sleeves (50) and the rods (54) for energy absorption in another mode.

Description: This invention relates to shaft vibration dampers for application in extreme temperature environments which exceed conventional damper capabilities, particularly in gas turbine engines. In gas turbine engines, rotor shaft vibrations are commonly controlled by squeeze-film dampers in which the damping medium is an oil film between fixed and floating housings of the damper. Applications for such dampers are limited to environments where ambient temperature around the damper does not exceed the maximum working temperature of the oil. A shaft vibration damper according to this invention is suitable for high-temperature environment applications beyond the range of usual oil film squeeze-film dampers. In addition, a shaft vibration damper according to this invention is also suitable for cryogenic environments below the temperature capabilities of usual squeeze-film dampers. This invention is a new and improved shaft vibration damper including a floating housing on a rotating shaft, a plurality of chambers in the floating housing arranged symmetrically around the axis of rotation of the shaft, and a plurality of impactors in respective ones of the chambers. Vibratory displacement of the shaft and floating housing induces impacts between the impactors and the corresponding chambers which impacts are accompanied by energy-absorbing, local plastic deformation of the impactors and the chambers. In a preferred embodiment of the damper according to this invention, the chambers are cylindrical bores in the floating housing parallel to the axis of rotation of the shaft and the impactors are cylindrical sleeves, see e.g. prior art document US-A-3 589 782. each having a tungsten rod therein. The sleeves are sealed at opposite ends and filled with a damping medium around the tungsten rods which is liquid at damper operating temperature. The damping medium is squeezed from between the tungsten rods and the sleeves for additional energy absorption as the impactors engage the chambers. The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a shaft vibration damper according to this invention; Figure 2 is a partially broken-away view taken generally along the plane indicated by lines 2-2 in Figure 1; Figure 3 is an enlarged view of a portion of Figure 1; and Figure 4 is a sectional view taken generally along the plane indicated by lines 4-4 in Figure 3. Referring to Figure 1, a schematically-represented rotor shaft 10, such as a gas turbine engine turbine shaft, is supported on a relatively stationary structure 12, such as an engine casing, by a schematically-represented bearing 14 for rotation about an axis 16. The bearing 14 includes an inner race 18 rotatable with the shaft 10, an outer race 20, and a plurality of rolling elements, i.e., bearing balls 22, between the inner and outer races. The centreline of shaft 10 normally coincides with axis 16. Dynamic unbalance, however, induces whirling, i.e., deflection of the shaft 10 perpendicular to the axis 16, characterised herein as radial vibratory displacement. A vibration damper 24 according to this invention is interposed between the outer race 20 of the bearing 14 and the stationary structure 12 to control radial vibratory displacement of the shaft 10. The shaft vibration damper 24, constructed for laboratory rig testing, includes a floating housing 26 having an annular rim 28, a cylindrical centre support 30, and a perforated radial web 32 between the rim 28 and centre support 30. The outer race 20 of the bearing 14 fits closely within the centre support 30 and butts against an internal radial flange 34 of the centre support 30. Bolts or other connecting devices, not shown, between the outer race 20 and the radial flange 34 rigidly connect the outer race to the floating housing 26. The rim 28 is disposed in a circular aperture 36 in the stationary structure 12. An outer radial flange 38 on the rim 28 is held by a retainer 40 bolted to the stationary structure 12. The retainer 40 prevents axial movement of the floating housing 26 in the direction of axis 16. Radial clearance, however, between outer flange 38 and the retainer 40 affords the floating housing 26 freedom of movement in a plane perpendicular to axis 16. In a gas turbine engine application, for example, a resilient connection is required between the rim 28 and the stationary structure 12 which is both rigid enough for structural integrity and flexible enough to accommodate radial vibratory displacement of the shaft 10. As seen best in Figures 1-2, the floating housing 26 further includes a plurality of cylindrical bores, i.e., chambers 42, in the rim 28 each located parallel to the axis 16. The chambers 42 are equally angularly spaced around the shaft 10 and are open at their opposite ends through respective ones of a pair of flat sides 44A, 44B of the rim. The chambers 42 are surrounded by a pair of seal grooves 45A, 45B in the flat sides 44A, 44B respectively. Referring to Figures 1-4, respective ones of a plurality of impactors, i.e., damper weights, 46 are disposed in corresponding ones of the chambers 42 and retained therein by a pair of rings 48A, 48B bolted to flat sides 44A, 44B, respectively, of the rim 28. A plurality of seals 49 in the grooves 45A, 45B are retained therein by rings 48A, 48B. Each impactor 46 includes a cylindrical sleeve 50 the diameter of which is of the order of 0.381 mm (0.015 inches) less than the diameter of the corresponding chamber 42. Each sleeve 50 is closed at its opposite ends by a pair of caps 52A, 52B. Respective ones of a plurality of solid tungsten rods 54 are disposed in corresponding ones of the sleeves 50 between the caps 52A, 52B. The diameters of the tungsten rods 54 are of the order of 0.254 mm (0.010 inches) less than the diameters of the corresponding sleeves 50. A high-temperature damping medium 56 fills the clearance between the tungsten rods 54 and the sleeves 50 in each impactor 46. The damping medium is liquid at the operating temperature of the damper 24 and may be oil for relatively low-temperature applications and a low-melting temperature metal such as lead for high-temperature applications. As the shaft 10 accelerates to a normal operating speed of the order of 40,000 RPM, dynamic unbalance in the shaft and/or elements rotating therewith induces radial vibratory displacement of the shaft in the plane of the damper 24. Vibratory displacement of shaft 10, transferred to the floating housing 26 through the bearing 14, induces collisions, i.e., impacts, between the impactors 46 and the chambers 42, which impacts initiate vibration-damping energy absorption in two modes. More particularly, the sleeves 50 stop moving when they impact the sides of the corresponding chambers 42. The tungsten rods 54, however, continue moving towards the sleeves 50 and, in so doing, squeeze the damping medium 56 from between the rods 54 and the sleeves 50. By resisting being squeezed from between the tungsten rods 54 and the sleeves 50, the damping medium 56 absorbs energy and damps the radial vibratory displacement of the shaft 10 in one mode. After the damping medium 56 is squeezed out, the tungsten rods 54 impact the sleeves 50 and, through the sleeves, the corresponding chambers 42. These impacts induce local plastic deformation of the rods 54 and the chambers 42, which local plastic deformation absorbs additional energy and damps the radial vibratory displacement of the shaft 10 in another mode. The damper 24 is useful in high and moderate temperature environments. For example, in moderate temperature environments characteristic of common squeeze-film dampers, the damping medium 56 may be oil. The advantage in using the damper 24 with oil is the elimination of piping, seals and the like usually associated with conventional squeeze-film dampers. In high-temperature environments beyond the limits of common squeeze-film dampers, the damping medium 56 may be a low-melting temperature metal such as lead which liquefies within the sleeves 50 as the engine is started. The advantage in using a low-melting temperature metal is the significantly higher maximum working temperature achievable. The damper 24 may also be useful in low or cryogenic temperature environments such as high-speed pumps in spacecraft propulsion systems which are below the operating temperature range of common oil film squeeze-film dampers. It will be apparent to those skilled in the art that a shaft vibration damper according to this invention could also be constructed for damping in only a single mode. That is, the impactors 46 could be solid so that the only mode of energy absorption is local plastic deformation of the impactors and the corresponding chambers 42 as described above.

Claims: A vibration damper (24) between a shaft (10) rotatable about an axis of rotation (16) and a relatively stationary structure (12), said vibration damper (24) comprising a floating housing (26), a bearing means (14) connecting said floating housing (26) to said shaft (10) for radial vibratory displacement thereof as a unit with said shaft (10) in a plane perpendicular to said axis of rotation (16) of said shaft (10), and retaining means (38,40) connecting said floating housing (26) to said stationary structure (12) and operative to accomodate said radial vibratory displacement of said floating housing (26) and said shaft (10), characterised in that said floating housing (26) includes a plurality of chambers (42) formed therein which are arranged symmetrically around the axis of rotation (16) of the shaft (10), and each of said chambers (42) contains an impactor (46) movably retained therein with a predetermined clearance between said impactor (46) and walls of the respective chamber (42) so that said impactor (46) can collide with the walls of the respective chamber (42) when said floating housing (26) vibrates as a unit with said shaft (10). A vibration damper (24) according to claim 1, characterised in that said bearing means (14) includes a bearing inner race (18) rigidly attached to said shaft (10), a bearing outer race (20), and a plurality of anti-friction elements (22) positioned between said inner race (18) and said outer race (20), said bearing outer race (20) being rigidly connected to a cylindrical centre support (30) of said floating housing (26). A vibration damper (24) according to claim 1 or 2, characterised in that each of said chambers (42) is a cylindrical bore in said floating housing (26), said cylindrical bore having a first diameter and being oriented in said floating housing (26) so that its longitudinal axis is parallel to said axis of rotation (16), and each of said impactors (46) is a metal cylinder having a second diameter less than said first diameter. A vibration damper (24) according to claim 3, characterised in that each of said impactors (46) includes a cylindrical metal sleeve (50) having an outside diameter equal to said second diameter, and a solid metal rod (54) movably retained within said metal sleeve (50) and having a diameter less than the inside diameter of said metal sleeve (50). A vibration damper (24) according to claim 4, characterised in that each of said impactors (46) contains a damping medium (56) surrounding said solid metal rod (54) and filling said metal sleeve (50), which damping medium (56) is liquid at the normal operating temperature of said damper (24). A vibration damper (24) according to claim 5, characterised in that said damping medium (56) is a low-melting temperature metal for high-temperature applications of said damper (24). A vibration damper (24) according to claim 6, characterised in that said damping medium is lead.

Inventors: FOX ALLEN EUGENE, KLUSMAN STEVEN ARLEN, NALE TIMOTHY ALAN, FOX, ALLEN EUGENE, KLUSMAN, STEVEN ARLEN, NALE, TIMOTHY ALAN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1991
Main classification: F01D5
IPC codes: F16F15, F16F7, F01D5, F16C27