Patent Publication Number: US-8529192-B2

Title: Thrust bearing shaft for thrust and journal air bearing cooling in a compressor

Description:
BACKGROUND 
     This application relates to a thrust bearing shaft incorporated into a compressor for use in supplying cabin air in an aircraft. 
     Compressors are known and include a motor driven to rotate a shaft and in turn drive a compressor rotor. Typically, there are bearings incorporated into a housing which support the shaft for rotation. One known type of bearing is an air bearing. 
     In one known air bearing, cooling air is brought into a bearing cooling inlet. The cooling air passes along thrust bearing surfaces, and then may pass between the shaft and various housing portions. The thrust bearing surfaces are spaced from a disk which rotates with a thrust shaft. The thrust shaft rotates with the motor rotor, and the compressor rotor. 
     The thrust bearing surfaces include a pair of surfaces on axial sides of the disk. Air passes along both of those surfaces. Air on one side of the disk passes along an outer periphery of the thrust shaft, and air on an opposed side of the disk will pass into a bore within the thrust shaft. This air passes through a plurality of holes formed in an internal ledge in the thrust shaft. A portion of this air can then pass radially outwardly through holes in a cylindrical portion of the shaft, while a separate portion continues along the bore of the thrust shaft. In the past, there has been insufficient cross-sectional flow area in the ledge to ensure adequate air flow. 
     SUMMARY 
     A thrust bearing shaft has an enlarged disk at one axial end to provide a rotating surface in a thrust bearing. A first cylindrical portion extends from the disk. A second cylindrical portion has a smaller diameter than the first cylindrical portion and extends from the first cylindrical portion to an end of the thrust shaft remote from the disk. The thrust shaft has a hollow bore with a ledge extending across the bore at a location within the first cylindrical portion. The ledge is formed with a central hole of a first hole diameter, and twelve air holes spaced circumferentially about the central hole. The twelve holes are formed of a second hole diameter, with a ratio of the first hole diameter to the second hole diameter being between 2.55 and 2.71. 
     In addition, a bearing assembly, a compressor, and a method of assembling a compressor are disclosed and claimed. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional view of a compressor incorporated into a cabin air supply. 
         FIG. 1B  shows a detail of the thrust bearings. 
         FIG. 2  is a perspective view of a thrust shaft. 
         FIG. 3  is a cross-sectional view through the  FIG. 2  shaft. 
         FIG. 4  is an end view of the  FIG. 2  shaft. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1A , a compressor  20  may be incorporated into a cabin air supply system  21  for passing air across the cabin of an aircraft. A rotor  22  receives air to be compressed from an inlet  24 , and passes it to a compressor outlet  26 . A motor  28  drives a tie rod, or driveshaft  30 , to rotate the rotor  22 . 
     An air bearing shaft  32  is positioned radially inward of journal bearings  34 . Air passes into a cooling inlet  36 , and between thrust bearing surfaces  38  and a thrust bearing disk  40  which is associated with a thrust shaft  39 . A portion of the air passes along the thrust bearing surfaces  38 , and then between the outer periphery of the thrust shaft  39  and journal bearings  41 . That air passes further downstream, and across the bearings  34 . Eventually, this air passes outwardly of outlet  50 . 
     As shown in  FIG. 1B , the thrust bearing surfaces  38  of  FIG. 1A  are defined between two housings  200 , and a plurality of corrugated bearing members  202 . Air passages are defined between the thrust bearing disk  40  and the corrugations  202 . In addition, further air passages are defined between the corrugations  202  and the housings  200 . 
     Air passes through the air passages, with a portion on a rear side of the disk  40  passing into an interior bore  300  of the thrust shaft  39 . Another portion passes over the journal bearings  41 . The shaft  30  has a nut  116  which extends through a hole  114  in a central ledge  121  in the thrust shaft  39 . 
     Flow passages within the thrust shaft  39  will be explained with reference to  FIGS. 2-4 . 
       FIG. 2  shows the thrust shaft  39  having the disk  40 , a first cylindrical portion  113 , a smaller second cylindrical portion  100  having a plurality of radially extending holes  102 , and seal members  104 . 
     As shown in  FIG. 3 , the ledge  121  has a plurality of air holes  112 , and a central bolt hole  114 . The relative sizes of the holes in  FIG. 3  are not to scale. A distance D 0  from an end  151  of second cylinder portion  100  to the beginning of the ledge  121  was 1.165″ (2.96 cm) in one embodiment. 
     As shown in  FIG. 4 , the diameter D 1  of the central bolt hole  114  was 0.495″ (1.257 cm) in this embodiment. In this embodiment, the diameter of the axial air holes  112 , D 2 , was 0.188″ (0.478 cm). A diameter D 3  to the inner periphery of the second cylindrical portion  100  was 1.1981 (3.04 cm) in one embodiment. 
     The holes  112  are all equally spaced about an axial centerline X, and thus by 30°. In embodiments, a ratio of D 1  to D 2  was between 2.55 and 2.71. In embodiments, a ratio of D 3  to D 2  was between 6.20 and 6.55. 
     As can be appreciated, the air that passes into the interior bore  300  of the thrust shaft  39  can pass through the holes  112 , and into a space  310  within the second cylindrical portion  100 . A portion of this air can pass radially outwardly through holes  102 , while another portion extends forwardly toward a motor rotor  320 . The increased volume of air flow passages provided by the holes  112  ensure the adequate flow of this air. 
     As can be appreciated, there are six holes  102 , and twelve air holes  112 . In the prior art, there were equal number of air holes in the ledge as the holes  102 . In this embodiment, the air holes  102  have a diameter of 0.150″ (0.381 cm), and thus are smaller than the air holes  112 . 
     In a method of assembling the compressor, the thrust shaft  39  is attached to the motor rotor  320  by initially having the motor rotor  320  placed in liquid nitrogen to reduce its size. Then, the end  151  of the thrust shaft is mounted on a surface on the motor rotor  320 . At the same time, the air bearing shaft  32  is connected to an opposed end of the motor rotor  320 , and an opposed end of the air bearing shaft  32  is secured to the compressor rotor  22 . Then, the tie shaft  30  is positioned through the rotor  22 , the shaft  32 , the rotor  320 , and the shaft  39 . The nut  116  is then tightened on the tie shaft  30  to secure all of the components together. The assembled construction can then be placed within the housing, with the housing portions  200  and corrugations  202  spaced from the disk  40 . 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.