Another form of lubrication is the 'elastohydrodynamic' lubrication. Note that the hydrodynamic pressure has no relationship at all to the engine oil pressure, except that if there is insufficient engine oil pressure to deliver the required copious volume of oil into the bearing, the hydrodynamic pressure mechanism will fail and the bearing(s) and journal(s) will be quickly destroyed.
Still further, the stiffness and damping coefficients of the dampers 71 can be selectively varied and controlled by changing the metal mesh material, geometry and mesh density depending upon the operating conditions encountered in the bearing chamber 56 vertical guide & thrust bearing during rotation of the shaft 55. The metal mesh dampers 71 also provide maximum damping at lower frequency ranges, wherein rotordynamic instability frequencies are significantly lower than the rotor synchronous frequency or shaft rotational frequency.
The leaf springs 41 rest on the force transmission piece 1. However, a pre-loading is given to the spring 41 by the support housing 2 which limits the travel of the spring 41 in the direction of the axis 7 of the shaft 6. When the sheets 3, under the action of a rotation of the shaft 6 with respect to the casing 5 separate from the shaft 6, they rest on the force transmission elements 1 which themselves rest on the leaf springs 41. The leaf springs 41 resist a very great separation of the sheets 3. They assure the radial stiffness of the bearing according to the present invention.
In another alternate embodiment for the bearing unit 49, the bearing 52 may be provided with a plurality of compliant structural dampers 54 on each bearing flange 66. More particularly, the annular flanges 66 may each be formed with pairs of circumferential mounting pockets or channels 98 and 99 which each receive a respective one of the dampers 54. These pockets 98 and 99 open radially outwardly about the circumference of the bearing flanges 66 but are axially closed on their inboard and outboard ends by side faces like side faces 86 and 87 described above.
Fig 2 - An externally pressurized thrust bearing looks and acts much like a double opposed face seal, when positioned on the high pressure side of a straight though centrifugal compressor, radial real estate on the thrust disc can be used as the balance piston shortening the required length of shaft enough to make a big improvement in rotor dynamics.
Bearing manufacturers that invested money licensing this design spend a good deal of time and money convincing its clients (fan manufacturers) that only bearings using this design can be called fluid dynamic.” Therefore, there is a tendency for fan manufacturers that use Matsushita's patented fluid dynamic bearings to think or even say that fans from other manufacturers using different fluid dynamic designs are fake” or not true” fluid dynamic bearings.
Generally, the fluid film hydrodynamic bearings disclosed in the above named patents operate on the principle that a rotating member such as a shaft or thrust runner and an adjacent element such as a smooth foil or the like establish and maintain a pressurized fluid film layer therebetween, the fluid film layer, sometimes referred to as a fluid film wedge, providing lubricated support for the rotating member.
Annular flanges 36, 38 at either side of the spring support extend radially outwardly from the inner spring support surface 32. These flanges support the spring support surface and ensure that the spring support does not slide axially with respect to the bearing.
The increasingly severe technological requirements led to considerable thermal and mechanical deformations and consequently compromise minimum film thickness in bearings ( Mansouri et al., 2007 ). The couple stresses fluid takes into account the properties of lubricants with additives.
The bearing 30 includes a cylindrical bearing wall 34 which defines inner and outer cavities 35 and 36 wherein the wall 34 includes ports 37 through which oil may flow between the cavities 35 and 36. The opposite ends of the bearing 30 include squeeze film dampers 39 defined by outer bearing surfaces 40 that respectively form an outer fluid film 41 of oil.
After startup, the rotation of the shaft 6 creates a hydrodynamic film of air which modifies the position occupied by the sheets 3 and causes a resumption of the effort at the level of the force transmission elements by the restraining elements 4, as for example the springs 40, 41, 42, 43. It is thus possible to achieve the bearings while having lesser precision of machining to that existing for the bearings of a conventional type.
This attachment of the foil and spring to key 35 provides ease in bearing manufacture and maintenance as well as facilitating removal of the foil and spring for replacement with foils and springs of differing properties for adjusting bearing properties such as load capacity, damping and the like.