Patent Application
20110064340
High speed rotating machines, such as auxiliary power units, may be subject to undesired vibrations during operation. For example, one type of auxiliary power unit may experience relatively high synchronous vibrations at speeds below the operating speed during transitional speed excursions. Such vibrations over time can result in the loss of engine structural integrity, including broken oil tubes, rear bearing turbine assembly failure and damage to the rotor assembly.
A squeeze film damper has been used at an interface between a housing and a bearing assembly to dissipate energy associated with “whirling” of the rotor bearing system. The squeeze film damper is intended to reduce rotor vibrations and bearing forces. A whirling condition exists when a rotational axis of the rotor orbits about the intended rotational axis provided by the housing. Despite the damping provided by the squeeze film, the eccentric movement or vibration of the rotor axis about the housing axis can cause damage or failure of rotor bearing system components.
A rotor bearing system is disclosed for a rotating machine. The rotor bearing system includes a housing having a bore that provides an inner surface. A bearing assembly is disposed within the bore and includes an outer surface. An annular cavity is provided radially between the outer surface and the inner surface. At least one protrusion extends radially outwardly from at least one of the inner and outer surfaces to an apex and into the annular cavity. A radial gap is arranged between the apex and the opposite surface from which the protrusion extends. In the disclosed example, the annular cavity is filled with an oil to provide a squeeze film damper between the housing and the bearing assembly. The protrusions exert a hydrodynamic preload on the bearing assembly, which reduces vibration during operation of the rotating machine.
These and other features of the disclosure can be best understood from the following specification and drawings, the following of which is a brief description.
An example auxiliary power unit (APU) 10 is illustrated in
Referring to
A rolling bearing element 27 is pressed into the outer cage 24. In one example, the rolling bearing element 27 is a ball bearing, although other bearings, such as needle bearings, can be used. The rolling bearing element 27 includes rolling elements 32 circumferentially retained by a bearing cage 34 and secured between inner and outer races 28, 30. A retainer 36, such as a circlip, is used to axially retain the outer race 30 relative to the outer cage 24. The shaft 18 is received in a press-fit relationship with the inner race 28. The inner race 28 is axially retained relative on the shaft 18 with a collar 38 that is secured to the shaft 18 by a fastener 40.
Referring to
The housing 22, liner 41, outer cage 24, piston rings 44 and outer race 30 are rotationally fixed relative to one another. The shaft 18 and inner race 28 are rotationally fixed relative to one another.
The housing 22 provides the axis A1 about which it is desirable to rotate the shaft 18. However, due to vibration of the bearing assembly 20 during operation of the APU 10, the shaft 18 may rotate about the axis A2 that is offset from the axis A1, best shown in
Circumferentially spaced lobes or protrusions 50 extend radially inwardly into the annular cavity 42 from at least one of the inner and outer surfaces 48, 47, which are generally cylindrical in shape. Each protrusion 50 is arranged circumferentially between a pair of holes 52. In the example shown, three protrusions 50 are circumferentially spaced from one another equally and extend from the inner surface 48 to an apex 51. It should be understood that protrusions may extend from the inner surface 47 instead or additionally. Moreover, more or fewer than three lobes can be used. The apexes 51 do not contact the opposite surface, the inner surface 47 in the example, when the axes A1, A2 are coaxial with one another (
The bearing assembly 20 is shown centered in the housing 22 in
Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.
