Abstract:
An oil lift pocket for a bearing surface having a plurality of channels in communication with a supply port. The plurality of channels may be formed in a substantially bow shaped configuration. Each channel may extend from a supply port and terminate at an end and away from the supply port. The oil lift pocket greatly reduces friction in slow turning operations and reduces babbitt delamination, dead zones, and nonuniform support and lift as well.

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to bearings and, more particularly, to oil lift pockets in bearing assemblies. 
     BACKGROUND 
     Large scale shafts often use a tremendous breakaway torque to begin to rotate. The rotors coupled to the shafts overcome friction at breakaway and overcome friction while rotating. Oil pockets of various descriptions have been used on bearing surfaces, such as babbitts, to reduce friction associated with shafts in contact with the bearing surfaces with varying degrees of success. In applications where a shaft is turned at relatively slow speeds, such as less than about 400 revolutions per minute (rpm), oil lift pockets have been used to reduce friction. Friction is reduced by injecting oil under high pressure, such as greater than about 500 psi, to reduce the load of the shaft on the bearing surface and thereby reduce the friction of the shaft on the bearing surface. Conventional configurations of oil lift pockets have reduced friction found in such configurations. However, use of such oil lift pockets has resulted in delamination of the babbitt and dead zones in which dirt and other contaminants have accumulated. Thus, a need exists for an oil lift pocket having minimal impact on the babbitt and without dead zones. 
     SUMMARY OF THE INVENTION 
     This invention relates to an oil lift pocket for a bearing assembly for reducing friction between a shaft or other element and a bearing surface. Oil may be injected under a pressure of between about 1,800 pounds per square inch (psi) and about 2,200 psig and at a flow rate of between about one gallon per minute and about four gallons per minute into the oil lift pocket. Injection of the oil may reduce friction, thereby reducing breakaway torque between about 60 fold and about 200 fold. Reduction of friction using the oil lift pocket enables smaller, lower cost turning motors to be used without requiring that other components be changed. The reduced friction equates to reduced breakaway torque associated with initial rotation of a shaft. The reduced friction also enables higher projected pad pressures to be used than conventional systems, thereby enabling smaller, more efficient bearings to be used during slow speed operations. 
     The oil lift pocket may include a cylindrical bearing surface and a supply port extending through the cylindrical bearing surface. The oil pocket may also include a plurality of channels extending from the supply port. For instance, the oil lift pocket may include first, second, third, and fourth channels extending from the supply port forming a bowtie shaped oil lift pocket without the channels contacting each other at the tips of the channels. The first channel may extend from the supply port and have a bend between a first end of the first channel and a second end of the first channel, wherein the second end of the first channel is in communication with the supply port. The oil lift pocket may also include a second channel extending from the supply port and having a bend between a first end of the second channel and a second end of the second channel such that the first end of the second channel terminates proximate to the first end of the first channel, wherein the second end of the second channel is in communication with the supply port. The oil lift pocket may include a third channel extending from the supply port and having a bend between a first end of the third channel and a second end of the third channel, wherein the second end of the third channel is in communication with the supply port. Also, the oil lift pocket may include a fourth channel extending from the supply port and having a bend between a first end of the fourth channel and a second end of the fourth channel such that the first end of the fourth channel terminates proximate to the first end of the third channel, wherein the second end of the fourth channel is in communication with the supply port. 
     Each of the channels may be formed from a first section and a second section, which may be divided by the bends in each channel. The sections of the channels may extend from the supply port at an angle relative to a longitudinal axis. The size of the angles between the sections of the channels and the longitudinal axis may vary or be the same. In at least one embodiment, each of the angles is the same. 
     An advantage of the oil lift pocket of this invention is that the coefficient of friction may be reduced between about 60 fold and about 200 fold, and the breakaway torque may be reduced as well. 
     Another advantage of this invention is that the reduction of the coefficient of friction enables smaller, lower cost turning motors to be used. 
     Yet another advantage of this invention is that the oil lift pocket allows for higher projected pad pressures to be used, which enables smaller, more efficient bearings to be used. 
     Still another advantage of this invention is that the oil lift pocket eliminates dead zones for contaminant accumulation, babbitt delamination, and nonuniform support and lift. 
     These and other embodiments are described in more detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention. 
         FIG. 1  is a perspective view of an oil lift pocket system of the instant invention installed in a turbine engine. 
         FIG. 2  is a frontal view of the oil lift pocket system shown in  FIG. 1  on an inner surface of a rotor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1–2 , this invention is directed to an oil lift pocket  10  for reducing friction in relatively slow turning applications, such as when a shaft  12  is rotating at speeds less than about 400 revolutions per minute (rpm). The oil lift pocket  10  of this invention may be capable of reducing friction, as quantified by the coefficient of friction, between 60 and 200 fold. Such a large reduction in friction enables smaller sized turning motors to be used in the same application and smaller, more efficient bearings to be used, resulting in increased efficiency. 
     As shown in  FIG. 1 , the oil lift pocket  10  may be formed on a bearing surface  14 . The bearing surface  14  may be, but is not limited to being, a babbitt or other appropriate structure, and may be formed from any appropriate material. The bearing surface  14  may include a plurality of oil channels  16  for containing pressurized oil for reducing friction on a shaft. More specifically, the bearing surface  14  may include channels  16  extending from a supply port  18  in a configuration that resembles a bowtie. However, in at least one embodiment, the channels  16  extend from the supply port  18  but do not contact each other. Instead, the channels  16  may form a bowtie shape in which the channel do not contact each other. 
     As shown in  FIG. 2 , a first channel  20  may extend from the supply port  18  and have a bend  22  between a first end  24  of the first channel  20  and a second end  26  of the first channel  20 . The first channel  20  may be in fluid communication with the supply port  18 . A second channel  28  may extend from the supply port  18  and have a bend  30  between a first end  32  of the second channel  28  and a second end  34  of the second channel  28 . The second channel  28  may be in fluid communication with the supply port  18 . The bend  30  may be configured such that the first end  32  of the second channel  28  terminates proximate to the first end  24  of the first channel  20  while the bend  30  of the second channel  28  and the bend  30  of the first channel  20  are remote from each other, as shown in  FIG. 2 . However, the bend  22  of the first channel  20  and the bend  30  of second channel  28  are positioned remote from each other, forming one side of the bow tie configuration of the oil lift pocket  10 . The first and second channels  20 ,  28  may, in at least one embodiment, be mirror images of each other. 
     The oil lift pocket  10  may also include third and fourth channels  36 ,  38  extending from the supply port  18 . In at least one embodiment, the channels  36 ,  38  may be in configuration that is a mirror image of the first and second channels  20 ,  28 . For instance, the third channel  36  may extend from the supply port  18  and have a bend  40  between a first end  42  of the third channel  36  and a second end  44  of the first channel  20 . The third channel  20  may be in fluid communication with the supply port  18  to receive oil from the supply port  18 . The fourth channel  38  may extend from the supply port  18  and have a bend  46  between a first end  48  of the fourth channel  38  and a second end  50  of the fourth channel  38 . The fourth channel  38  may be in fluid communication with the supply port  18 . The bend  46  may be configured such that the first end  48  of the fourth channel  38  terminates proximate to the first end  42  of the third channel  36  while the bend  46  of the fourth channel  38  and the bend  40  of the third channel  36  are remote from each other, as shown in  FIG. 2 . However, the bend  40  of the third channel  36  and the bend  46  of second channel  38  are positioned remotely from each other, forming one side of the bow tie configuration of the oil lift pocket  10 . 
     In at least one embodiment, the first and fourth channels  20 ,  38  may extend from the supply port  18  generally opposite from each other. In addition, the second and third channels  28 ,  36  may extend from the supply port  18  generally opposite from each other. In at least one embodiment, the first, second, third, and fourth channels  20 ,  28 ,  36 , and  38  may extend from the supply port  18  at locations on the supply port that are generally equidistant from each other. 
     As shown in  FIG. 1 , the channels  16  may have portions of themselves that are positioned at angles relative to each other. For instance, the bend  22  in the first channel  20  may form a first section  52  proximate the first end  24  at a first angle  54  relative to a longitudinal axis  56 , and the bend  30  in the second channel  28  may form a second section  58  proximate the second end  26  of the second channel  28  at the first angle  54  relative to the longitudinal axis  56 . The bend  30  in the second channel  28  may form a first section  60  proximate the first end  32  at a second angle  62  relative to the longitudinal axis  56 , and the bend  22  in the first channel  20  may form a second section  64  proximate the second end  26  of the first channel  20  at the second angle  62  relative to the longitudinal axis  56 . The bend  40  in the third channel  36  may form a first section  66  proximate the first end  42  at a third angle  68  relative to the longitudinal axis  56  and the bend  46  in the fourth channel  38  may form a second section  70  proximate the second end  50  of the fourth channel  38  at the third angle  68  relative to the longitudinal axis  56 . The bend  46  in the fourth channel  38  may form a first section  72  proximate the first end  48  at a fourth angle  74  relative to the longitudinal axis  56 , and the bend  40  in the third channel  36  forms a second section  76  proximate the second end  50  of the first channel  20  at the fourth angle  74  relative to the longitudinal axis  56 . The first, second, third, and fourth angles,  54 ,  62 ,  68 , and  74  may be different values, or one or more of the angles  54 ,  62 ,  68 , and  74  may have the same values. In at least one embodiment, the first, second, third, and fourth angles,  54 ,  62 ,  68 , and  74  have the same values. The first, second, third, and fourth angles,  54 ,  62 ,  68 , and  74  may be between about 45 degrees and 60 degrees. Bearings having a relatively short length may have angles  54 ,  62 ,  68 , and  74  that are about 45 degrees, and bearings having a relatively long length may have angles  54 ,  62 ,  68 , and  74  that are about 60 degrees. 
     The supply port  18  may have any appropriate configuration and be sized according to the anticipated flow rate of oil. In at least one embodiment, a counterbore  78  may be positioned concentrically with the supply port  18 . The channels  20 ,  28 ,  36 , and  38  may have varying depths depending on the application. In at least one embodiment, the channels  20 ,  28 ,  36 , and  38  may have a depth of about 0.06 inches. 
     During operation, oil is injected into the oil lift pocket  10  to reduce friction on a shaft in contact with the bearing surface  14 . In at least one embodiment, oil is injected into the supply port  18  where the oil flows into the channels  16 . The oil may be injected under a pressure of between about 1,800 pounds per square inch (psi) and about 2,200 psig and at a flow rate of between about one gallon per minute and about four gallons per minute. Injection of the oil may reduce friction, thereby reducing breakaway torque by between about 60 and 200 fold. The configuration of the pocket does not contribute to the accumulation of contaminants. 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.