Abstract:
A gas turbine engine system includes an electric starter motor which utilizes a partially hollow or cupped shaped rotor. Space is provided inside the rotor to fit the required clutch, bearings, and drive shaft. A short package is provided due to the telescoped architecture while retaining the maximum length for electromagnetics.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a gas turbine engine, and more particularly to a compact electric starter motor therefor.  
           [0002]    Current starting systems for marine and industrial gas turbine engines includes pneumatic and hydraulic start systems. While these systems are effective there may be certain limitations and drawbacks to each. Some of these limitations include: high failure rates; usage of high pressure fluids; lack of accurate speed and torque control during starting, restarting and motoring cycles; and a relatively large overall system space requirements.  
           [0003]    Electrical starter systems offers several advantages over pneumatic or hydraulic start systems including: lower overall system volume and cost; higher reliability; improved speed/torque control for starting, re-engagement, and motoring; improved self test and health monitoring; and elimination of potentially hazardous fluids. However, conventional electrical start systems that generate sufficient power to rotate the gas turbine system are relatively large and cumbersome.  
           [0004]    A conventional electrical starter includes a central rotor shaft surrounded by a stationary winding (stator). The rotor is supported at each end by bearings mounted outside the axial envelope of the stator. When this arrangement is combined with a separate clutch, the length of the combined shaft, clutch and motor assembly exceeds the axial length available adjacent an industrial gas turbine engine gearbox.  
           [0005]    Accordingly, it is desirable to provide a relatively compact electrical starter system that will reasonably fit and operate on the accessory gearbox of a gas turbine engine.  
         SUMMARY OF THE INVENTION  
         [0006]    The gas turbine engine system according to the present invention integrates the clutch and the motor together in a unique fashion that reduces the overall size and increases the power density of the electric starter motor. This results in a package that can reasonably fit on an accessory gearbox and provide the required functions and power density.  
           [0007]    This electric starter motor design architecture utilizes a partially hollow or cupped shaped rotor. Space is therefore provided inside the rotor to fit the required clutch, bearings, and drive shaft. A short package is provided due to the telescoped architecture while retaining the maximum length for electromagnetics.  
           [0008]    The present invention therefore provides a greater power density for a given volume electric starter motor package. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0010]    [0010]FIG. 1 is a general schematic view of a gas turbine engine system;  
         [0011]    [0011]FIG. 2 is a perspective view of an electric starter motor designed according to the present invention;  
         [0012]    [0012]FIG. 3 is a longitudinal sectional view of the electric starter motor taken along line  3 - 3  of FIG. 2;  
         [0013]    [0013]FIG. 4 is a sectional view of the electric starter motor taken along line  4 - 4  of FIG. 3;  
         [0014]    [0014]FIG. 5 is a sectional view of the electric starter motor taken along line  5 - 5  of FIG. 3; and  
         [0015]    [0015]FIG. 6 is a chart comparing a 200 HP electric starter motor designed according to the present invention as compared to a conventional 200 HP starter motor in terms of weight, length and overhung moment.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    [0016]FIG. 1 illustrates a schematic block view of a gas turbine engine system  10  typical of industrial or marine usage. The system  10  includes a gas turbine engine  12  an accessory gearbox  14  mounted to the gas turbine engine  12  to initiate rotation thereof and an electric starter motor  16  operable to drive the accessory gearbox  14 . It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention.  
         [0017]    The starter motor  16  drives the accessory gearbox  14  through a clutch  18  which is preferably contained within a housing  20  of the electric starter motor  16 . The housing  20  is relatively compact such that the starter motor  16  will fit completely upon the accessory gear box  14 . A relatively compact system  10  which reduces packaging space is thereby provided. The system  10  may therefore be located in heretofore unavailable spaces.  
         [0018]    Referring to FIG. 2, the electric starter motor  16  includes a base  22 , flange  55 , and a power junction box  24  mounted to the housing  20 . The flange  55  allows direct mounting to the accessory gear box  14 . The base  22  allows auxiliary mounting to the gas turbine  12  or other supporting structure. The junction box  24  is mounted to the housing  20  longitudinally opposite an input shaft  26  which defines a longitudinal axis A of the electric starter motor  16 .  
         [0019]    Referring to FIG. 3, a sectional view along the axis of rotation A through the housing  20  of the starter motor  16  is illustrated. A rotor shaft  28  drives the input shaft  26  through the clutch  18 . The clutch  18  is preferably a high speed overrunning clutch such as that manufactured by Hilliard Corporation™ of Elmira N.Y. The clutch  18  is mounted within a clutch cavity  32  formed within an annular housing portion  34  of the housing  20 . Preferably, the annular housing portion  34  is at least partially conical and preferably extends at least partially within a hollow rotor  36  mounted to the rotor shaft  28 .  
         [0020]    The hollow rotor  36  includes a base portion  38  and an annular rotor portion  40  extending from the base portion  36 . The base portion  38  is substantially transverse to axis A and the annular rotor portion  40  is substantially parallel to the axis A. In other words, the rotor  36  is substantially cup shaped such that the annular rotor portion  40  at least partially contains the annular housing portion  34  (also illustrated in FIG. 4). Various fluid passageways  43  (FIG. 5) communicate fluids to and from the cavities  32 ,  42  to assume proper lubrication, cooling, and airflow. It should be understood that numerous passageway configurations will benefit from the present invention.  
         [0021]    The rotor  36  rotates with the rotor shaft  28  within a rotor cavity  42 . The clutch cavity  32  and the rotor cavity  42  are preferably separate fluid cavities. The cavities  32 ,  42  contain a fluid lubricant or the like. As the cavities  32 ,  42  are separate particular fluids may be contained within each cavity.  
         [0022]    The shaft  28  is mounted to the annular housing portion  34  through a bearing assembly  44   a  and  44   b . The bearing assembly  44   a  and  44   b  are located at least partially within the annular rotor portion  40 . That is, the bearings  44   a ,  44   b  are contained within an outer axial envelope defined by the rotor  36 . An exceeding compact starter motor  16  is thereby provided as the starter motor  16  is essentially telescoped in on itself because of the hollow rotor  36 .  
         [0023]    A permanent magnet  46  is mounted to the outer surface  48  of the rotor  36  through adhesion and/or cylindrical sleeve  49  or the like. It should be understood that a contiguous or segmented magnet will benefit from the present invention. The permanent magnet  46  takes full advantage of the axial length of the housing which provides a relatively powerful motor in spite of the telescoped architecture. Annular rotor portion  40  also functions as the magnetic “back iron” for the magnets, completing the magnetic flux path with the rotor portion on the motor. The rotor rotates within a stator  50  as generally known. The stator  50  includes windings  52  within a metallic lamination  54 . Windings  52  preferably include copper wire or other conductive filaments.  
         [0024]    It should be understood that various stator constructions will benefit from the geometry of the present invention. The starter motor  16  having rotor architecture of the present invention, however, provides advantages in terms of weight, length and overhung moment as compared to a conventional starter motor. For example only, FIG. 6 compares a 200 HP motor designed according to the present invention to a conventional  200  HP. The motor architecture of the present invention therefore allows for a unique integration of the clutch and a higher power density which provides the functionality and required power in a package that is far smaller than a typical electric motor and clutch arrangement.  
         [0025]    The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.