Abstract:
A connection for a rotating machine according to an exemplary aspect of the present disclosure includes an interface axially between and adjacent to a first interference fit and a second interference fit.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to an air-turbine starter used to start gas turbine engines, and more particularly to a shaft connection therefor. 
         [0002]    Many relatively large turbine engines, including turbofan engines, may use an air turbine starter (ATS) to initiate turbine engine rotation. The ATS includes a turbine section coupled to an output section mounted within a housing. The turbine section is coupled to a high pressure fluid source, such as compressed air, to drive the output section. The turbine section drives the output section through a gear system. Thus, when the high pressure fluid source impinges upon the turbine section, the output section powers the turbine engine. 
       SUMMARY 
       [0003]    A connection a rotating machine according to an exemplary aspect of the present disclosure includes an interface axially between and adjacent to a first interference fit and a second interference fit. 
         [0004]    A gear according to an exemplary aspect of the present disclosure includes a spline pitch inner diameter axially between and adjacent to a gear inboard pilot diameter and a gear outboard pilot diameter. 
         [0005]    A turbine rotor shaft according to an exemplary aspect of the present disclosure includes a spline pitch outer diameter axially between and adjacent to a turbine rotor shaft inboard pilot diameter and a turbine rotor shaft outboard pilot diameter. 
         [0006]    An air turbine starter according to an exemplary aspect of the present disclosure includes a gear mounted to a turbine rotor shaft, the turbine rotor and the gear defines a connection having an interface axially between and adjacent to said interference fit and a second interference fit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0008]      FIG. 1  is a general schematic view of an air turbine starter (ATS) used to initiate the rotation of a larger turbine through an accessory gearbox; 
           [0009]      FIG. 2  is a side perspective view of a turbine rotor shaft; 
           [0010]      FIG. 3  is an expanded view of an interface for the ATS; 
           [0011]      FIG. 4  is a side sectional view of a sun gear mountable to the turbine rotor shaft; 
           [0012]      FIG. 5  is an expanded side sectional view of the turbine rotor shaft; 
           [0013]      FIG. 6  is an expanded view of a spline of the turbine rotor shaft; and 
           [0014]      FIG. 7  is a perspective sectional view of a spline of the turbine rotor shaft. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  schematically illustrates an exemplary air turbine starter (ATS)  20  that is used to initiate the rotation of a larger turbine  22 , such as a turbofan engine through an accessory gearbox  24 . The ATS  20  generally includes a housing assembly  30  that includes at least a turbine section  32  and an output section  34 . The turbine section  32  includes a turbine wheel  36  with a plurality of blades  38 , a hub  40 , and a turbine rotor shaft  42  ( FIG. 2 ). The turbine rotor shaft  42  is coupled to a starter output shaft  44  though a gear system  46  (illustrated schematically) such as a planetary gear system. It should be appreciated that the present application is not limited to use in conjunction with a specific type of rotating machine. Thus, although the present application is, for convenience of explanation, depicted and described as being implemented in an air turbine starter, it should be appreciated that it can be implemented in numerous other machines including, but not limited to, a gas turbine engine, an auxiliary power unit, a turbo charger, a super charger, an air cycle machine, an alternator, an electric motor, an electric generator, an integrated constant speed drive generator and gearboxes of various types with an interface which is to be closely controlled. 
         [0016]    The ATS  20  transmits relatively high loads through the gear system  46  to convert pneumatic energy into mechanical energy for turbine engine starting. The planetary gear system  46  generally includes a sun gear  48  mounted to the turbine rotor shaft  42  to drives a planet gear set  50  (illustrated schematically) which, in turn, drive a single ring gear  52  (illustrated schematically) connected to the starter output shaft  44 . To minimize ATS size and weight, precise alignment of the planetary gear system  46  facilitates the smallest, lightest weight gears capable of desired life requirements. The sun gear  48  on the turbine rotor shaft  42  should thereby be precisely aligned due to the high transmitted load. 
         [0017]    With reference to  FIG. 3 , a connection  60  is utilized to mechanically mount the sun gear  48  upon the turbine rotor shaft  42 . In the disclosed non-limiting embodiment, the connection  60  includes an interference fit  62 A,  62 B and an interface  66  such as a splined interface to transfer torque; however, other connections such as single square keys, multiple square keys, or Woodruff keys may alternatively or additionally be utilized. The splined interface distributes the transmitted torque around the circumference of the turbine rotor shaft  42  rather than concentrating at the locations of keys. To maintain a precise alignment of the sun gear  48  on the turbine rotor shaft  42 , the sun gear  48  and the turbine rotor shaft  42  are configured to provide the interference fit  62 A,  62 B at each end section  48 A,  48 B of the sun gear  48  to flank a conventional interface  66 . 
         [0018]    The interference fit  62 A,  62 B may be defined to provide an interference for all operating conditions yet minimizes the magnitude of interference which must be overcome during assembly of the ATS  20 . The interface  66  may be defined by a spline  42 S ( FIGS. 2 and 5 ) on the turbine rotor shaft  42  and a spline  48 S of the sun gear  48  ( FIG. 4 ) to provide the interface  66  which, as typical, may have some backlash. 
         [0019]    In one non-limiting embodiment, the interference fits  62 A,  62 B are respectively defined by an inboard pilot diameter  42 A and an outboard pilot diameter  42 B. The inboard pilot diameter  42 A is larger in diameter than the major diameter of the spline  42 S on the turbine rotor shaft  42  while the outboard pilot diameter  42 B is smaller than the minor diameter of the spline  42 S ( FIG. 5 ). That is, the inboard pilot diameter  42 A is larger in diameter than the major diameter of the spline  42 S on the turbine rotor shaft  42  while the outboard pilot diameter  42 B is smaller than the minor diameter of the spline  42 S to facilitate a unidirectional assembly (rotor shaft  42  inserted from left to right in the Figure). It should be understood that other relationships may alternatively be provided. The outboard pilot diameter  42 B may alternatively be only slightly smaller than the rotor shaft spline major diameter (diameter of the tips of the teeth) which may result in “remnant” spline teeth across all or a portion width of the outboard pilot diameter  42 B; however, this would be acceptable for operational usage. 
         [0020]    The inboard interference fit  62 A is defined by a turbine rotor shaft dimension IPD ( FIG. 6 ) and a gear inboard pilot diameter dimension GIPD ( FIG. 4 ). The outboard interference fit  62 B is defined by a turbine rotor shaft dimension OPD and a gear outboard pilot diameter dimension GOPD ( FIG. 4 ). The turbine rotor shaft  42  also defines a spline major diameter dimension TS. In one non-limiting dimension embodiment, IPD is approximately 0.59inches (14.99 mm); OPD is approximately 0.50 inches (12.7 mm); and TS is 0.575 inches (14.6 mm). 
         [0021]    The gear inboard pilot diameter dimension GIPD, the gear outboard pilot diameter dimension GOPD, and a spline minor diameter of the gear spline are defined by dimension GS. In one non-limiting dimension embodiment, GIPD is approximately 0.59 inches (14.99 mm); GOPD is approximately 0.50 inches (12.7 mm) and GS is approximately 0.525 inches (13.3 mm). 
         [0022]    The closely controlled radial location relationship between the pilot diameters with respect to each other, and also to the pitch diameter of the sun gear  48 , ensures proper location and alignment. That is, the double interference pilot fit ensures the sun gear  48  does not tilt when an end face of the sun gear  48  seats against an end face of an adjacent component C mounted to the turbine rotor shaft  42  ( FIG. 7 ). It should be appreciated that the component C is representative of various components which may be mounted to the turbine rotor shaft  42 . An arrangement which does not use two interference pilots achieves a potentially less effective alignment because the gear may be subject to tilting when clamped in place by a component D such as a nut opposite the component C ( FIG. 7 ). This may result in adverse gear life. 
         [0023]    It should also be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
         [0024]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
         [0025]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.