Abstract:
An example gear arrangement includes a gearbox shaft and a journal shaft. The journal shaft establishes an opening that receives an end portion of the gearbox shaft. The gearbox shaft is configured to rotate the journal shaft. The journal shaft is configured to selectively rotatably couple with another shaft. The journal shaft is allowed to align to the bearing surface while the gearbox shaft allows for misalignment between the accessory and gearbox drive.

Description:
BACKGROUND 
       [0001]    This disclosure relates generally to a gear arrangement. More particularly, this disclosure relates to a gear arrangement that is configured to selectively transmit a rotational input to a turbomachine rotor. 
         [0002]    Turbomachines, such as gas turbine engines, are known. A typical turbomachine includes multiple sections, such as a fan section, a compression section, a combustor section, and a turbine section. Many turbomachines, particularly gas turbine engines, have large rotors in the compression section that must be accelerated to high rotational speeds before the rotors sufficiently compress enough air to sustain operation of the turbomachine. A motor separate from the turbomachine drives a rotor shaft to accelerate the rotors. Some motors are used as generators after the turbomachine is self-sustaining. The generated power is supplied to various components, such as components on an aircraft. 
         [0003]    A gearbox shaft from the motor is moveable between a position coupled with the rotor shaft and a position decoupled from the rotor shaft. In the coupled position, the gearbox shaft and the rotor shaft are rotatably connected. In the decoupled position, the gearbox shaft and the rotor shaft are independently rotatable. An internal failure mode within the motor or the engine may necessitate decoupling the gearbox shaft from the rotor shaft, for example. The decoupling ensures that errors or failure modes are not communicated between the gearbox shaft and the rotor shaft. The motor shaft typically continues to rotate even when decoupled from the gearbox shaft. A gear arrangement accommodates the rotating gearbox shaft whether the gearbox shaft is coupled with the rotor shaft or decoupled from the rotor shaft. The gearbox shaft can move eccentrically relative to the rotor shaft. 
       SUMMARY 
       [0004]    An example gear arrangement includes a gearbox shaft and a journal shaft. The journal shaft establishes an opening that receives an end portion of the gearbox shaft. The gearbox shaft is configured to rotate the journal shaft. The journal shaft is configured to selectively rotatably couple with another shaft. 
         [0005]    An example gas turbine engine gearbox arrangement includes an output shaft and a gearbox shaft. The gearbox shaft has a first end rotatably coupled to an accessory gearbox. A journal shaft is received over an opposing second end of the gearbox shaft. The journal shaft is configured to rotate together with the gearbox shaft. The journal shaft is further configured to selectively rotatably engage the output shaft to drive a rotor shaft of the gas turbine engine. 
         [0006]    An example method of rotating a gas turbine engine rotor includes rotating a gearbox shaft. The method rotates a journal shaft with the gearbox shaft. The journal shaft is received over an end of the gearbox shaft. The method also selectively couples the journal shaft to another shaft that rotates a rotor. 
         [0007]    These and other features of the disclosed examples can be best understood from the following specification and drawings, the following of which is a brief description: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a schematic view of an engine and a motor-generator of an aircraft. 
           [0009]      FIG. 2  shows an example rotor assembly of the  FIG. 1  engine. 
           [0010]      FIG. 3  shows a close-up section view of an example gear arrangement within the  FIG. 1  aircraft having a gearbox shaft in a connected position. 
           [0011]      FIG. 4  shows a close-up section view of the  FIG. 3  gear arrangement having the gearbox shaft in a disconnect position. 
           [0012]      FIG. 5  shows a perspective view of a retainer assembly used in the  FIG. 3  gearbox. 
           [0013]      FIG. 6  shows a section view at line  6 - 6  of  FIG. 5 . 
           [0014]      FIG. 7  shows a perspective view of an example journal shaft used in the  FIG. 3  gearbox. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to  FIGS. 1-2 , a gas turbine engine  10  propels an aircraft  12 . The gas turbine engine  10  is an example type of turbomachine. 
         [0016]    The example gas turbine engine  10  includes (in serial flow communication) a fan section  14 , a low pressure compressor  18 , a high pressure compressor  22 , a combustor  26 , a high pressure turbine  30 , and a low pressure turbine  34 . The gas turbine engine  10  is circumferentially disposed about an engine centerline X. 
         [0017]    During operation, air is pulled into the gas turbine engine  10  by the fan section  14 . Some of the air moves through a flow path  36  to a core of the gas turbine engine  10 . The air moving through the flow path  36  is pressurized by the compressors  18  and  22 , mixed with fuel, and burned within the combustor  26 . The turbines  30  and  34  extract energy from the hot combustion gases flowing from the combustor  26 . 
         [0018]    As known, the compressors  18  and  22  include a rotor assembly  40  having rotor blades  44  connected to a rotor shaft  42 . Rotating the rotor shaft  42  rotates the rotor blades  44 . The rotor blades  44 , when rotated, compress the air moving through the flow path  36 . 
         [0019]    In a two spool design, the high pressure turbine  30  utilizes the energy extracted from the hot combustion gases to power the high pressure compressor  22  through a high speed shaft  38 , and the low pressure turbine  34  utilizes the extracted energy from the hot combustion gases to power the low pressure compressor  18  and the fan section  14  through a low speed shaft  42 . 
         [0020]    The examples described in this disclosure are not limited to the two spool engine architecture described, however, and may be used in other architectures, such as single spool axial design, a three spool axial design, and still other architectures. Further, although the examples described herein are described with regard to the gas turbine engine  10 , those having skill in this art and the benefit of this disclosure will understand that other examples include other types of turbomachines. 
         [0021]    The example aircraft  12  includes a motor-generator  50  that is used to rotate the rotor assembly  40  of the engine  10  during start-up of the engine  10 . The accessory gearbox  52  is also used to drive the motor-generator  50  when the motor-generator  50  is operating in a generate mode. The motor-generator  50  provides a rotational input to the accessory gearbox  52  through a gear arrangement  54 . 
         [0022]    The example motor-generator  50  accelerates the rotor assembly  40  during start-up of the engine  10 . The motor-generator  50  continues to drive rotation of the rotor assembly  40  until the rotor assembly  40  reaches a speed capable of compressing enough air to sustain operation of the engine  10 . In this example, the motor-generator  50  operates as a generator after the engine  10  has reached a self-sustaining speed. 
         [0023]    Referring to  FIG. 3  with continuing reference to  FIGS. 1-2 , the example gear arrangement  54  includes a gearbox shaft  58  that is used to drive the accessory gearbox  52 . 
         [0024]    The example gear arrangement  54  selectively couples the accessory gearbox  52  to the engine  10 . The selective coupling ensures that the motor-generator  50  can be disconnected from the engine  10  if a failure occurs. In a coupled position, the gearbox shaft  58 , the rotor shaft  42 , and the disconnect shaft  82  are rotatably connected. In a decoupled position, the gearbox shaft  58  and the disconnect shaft  82  are independently rotatable. Given the disconnect shaft  82  is still coupled to the rotor shaft  42 , rotor shaft  42  is also independently rotatable from the gearbox shaft  58 . 
         [0025]    In some examples, the motor-generator  50  is coupled to the engine  10  when the motor-generator  50  operates as a generator. In such examples, rotational input is then supplied to the motor-generator  50  from the engine  10 . When operating as a generator, the motor-generator  50  provides electrical power to other areas of the aircraft  12  through the aircraft electrical system. Integrated drive generators and variable frequency generators are examples of the motor-generator  50 . 
         [0026]    When the motor-generator  50  operates as a motor, the motor-generator  50  rotates the gearbox shaft  58  to rotate the rotor assembly  40  of the engine  10 . In this example, the rotors of the motor-generator  50  are press fit directly to the rotor shaft  42 . 
         [0027]    In other examples, the motor-generator  50  is decoupled from the engine  10  in the event of a failure. 
         [0028]    An end  62  of the gearbox shaft  58  is received within a journal shaft  66 . In this example, the journal shaft  66  establishes an opening  70  configured to receive the end  62  of the gearbox shaft  58 . The journal shaft  66  is cup-shaped in this example. 
         [0029]    The other end  64  of the gearbox shaft  58  is rotatably coupled to the accessory gearbox  52 . The diameter of the end  64  is larger than the end  62  in this example. The ends  62  and  64  are each larger than an axially central portion of the gearbox shaft  58 , which causes the gearbox shaft  58  to have a dogbone configuration. The slimmed central portion acts as a shear section or torque limiter in this example. 
         [0030]    The journal shaft  66  and the gearbox shaft  58  are configured to rotate together. That is, the journal shaft  66  is configured to rotate the gearbox shaft  58 , and the gearbox shaft  58  is configured to rotate the journal shaft  66 . In this example, the gearbox shaft  58  and the journal shaft  66  rotate together when the accessory gearbox  52  is coupled to the engine  10  and when the accessory gearbox  52  is decoupled from the engine  10 . 
         [0031]    When the accessory gearbox  52  is coupled to the engine  10 , a jaw assembly  74  on the journal shaft  66  engages a corresponding jaw assembly  78  on a disconnect shaft  82 . When the jaw assembly  74  is engaged with the jaw assembly  78 , the disconnect shaft  82  rotates together with the journal shaft  66  and is connected to the rotor shaft  42 . 
         [0032]    In this example, the disconnect shaft  82  and the rotor shaft  42  are configured to rotate together. That is, the disconnect shaft  82  is configured to rotate the rotor shaft  42 , and the rotor shaft  42  is configured to rotate the disconnect shaft  82 . 
         [0033]    Decoupling the motor-generator  50  from the engine  10  is necessary when a failure in the aircraft  12  is discovered, for example. When the engine  10  is decoupled, the jaw assembly  74  on the journal shaft  66  is disengaged from the jaw assembly  78  on the disconnect shaft  82 . When the jaw assembly  74  is disengaged from the jaw assembly  78 , the disconnect shaft  82  is rotatable separate from the journal shaft  66 . 
         [0034]    The disconnect shaft  82  moves back and forth along in a direction X 1  as the jaw assembly  74  and  78  move between engaged and disengaged positions. A person having skill in this art and the benefit of this disclosure would understand how to incorporate suitable mechanisms, such as a worm gear (not shown), within the gear arrangement  54  for moving the jaw assembly  74  and  78  between engaged and disengaged positions. 
         [0035]    The example journal shaft  66  slides against an axial/radial thrust bearing  90  and an axial thrust bearing  94  as the journal shaft  66  moves back and forth in the direction X 1 . The example bearings  90  and  94  are carbon-based bearings and include steel on a thrust surface  96  and  22  to facilitate resisting thrust loads urging the journal shaft  66  toward the disconnect shaft  82  or engine  10 . An outer wall  100  of the journal shaft  66  contacts the bearing  90  in this example. 
         [0036]    During disengagement of the journal shaft  66  from the disconnect shaft  82 , the journal shaft  66  forces a hardened thrust washer  102  against a carbon face  104 . This is due to disconnect forces associated with separating disconnect jaws  74  from  78 . In this example, a spacer  106  holds the hardened thrust washer  102  relative to the journal shaft  66 . The thrust washer  102  is also keyed to the shaft  66  so they rotate together in this example. 
         [0037]    Referring to  FIGS. 5-7  with continuing reference to  FIGS. 3-4 , the bearings  90  and  94  are carried by a retainer assembly  92  that rotates together with the rotor shaft  42 . The retainer assembly  92  and the bearings  90  and  94  rotate together with the journal shaft  66  when the jaw assembly  74  of the journal shaft  66  is engaged with the jaws  78  of the disconnect shaft  82 . 
         [0038]    The example journal shaft  66  includes a flange  93  having a diameter d 1 . The flange  93  contacts the bearing  94  to oppose thrust loads. In this example, the diameter d 1  is greater than any diameter of the gearbox shaft  58 . This diameter is larger to reduce bearing pressure*velocity (PV) loads, for example. The flange  93  opposes eccentric movement of the gearbox shaft  58  transferring to the journal shaft  66 . This facilitates the journal shaft  66  maintaining an aligned position relative to the bearings  90  and  94  during rotation even though the gearbox shaft  58  may move eccentrically relative to the journal shaft  66 . 
         [0039]    The direction X 1  corresponds to the rotational axis of the journal shaft  66  in this example. When rotated, the journal shaft  66  rotates about the axis X 1  when the jaw assembly  74  and  78  are in an engaged position and when the jaw assembly  74  and  78  are in the disengaged position. 
         [0040]    In this example, the end  62  of the gearbox shaft  58  includes a plurality of splines  98 . An inner wall  106  of the journal shaft  66  includes a corresponding plurality of splines  108 . The splines  98  rotate against the splines  108  to rotate the journal shaft  66  with the gearbox shaft  58 . The splines  108  rotate against the splines  98  to rotate the gearbox shaft  58  with the journal shaft  66 . 
         [0041]    The splines  108  and  98  extend axially for a length  1 . The length  1  facilitates accommodating fluctuations in the position of the gearbox shaft  58  relative to the position of the journal shaft  66 . Such as movements in a direction y relative to the journal shaft  66 . Movement of the gearbox shaft  58  in the direction y relative to the journal shaft  66  is referred to as an eccentric movement of the gearbox shaft  58  relative to the journal shaft  66 , for example. 
         [0042]    When the gearbox shaft  58  is rotating eccentrically relative to the journal shaft  66 , the rotational axis of the gearbox shaft  58  is transverse to the rotation axis of the journal shaft  66 . The example gearbox shaft  58 , due (in part) to the length  1  of the splines  108  and  98 , accommodates eccentric movements of the gearbox shaft  58 . The splines  98  maintain contact with the splines  108  even if the splines  98  are tilted relative to the splines  108 . 
         [0043]    Features of the disclosed examples include a journal shaft maintaining contact axially and radially against carbon bearings while accommodating eccentric movements of the gearbox shaft relative to the journal shaft. Another feature of the disclosed examples include adding steel to carbon bearings, and specifically the thrust surfaces of the carbon bearings, to react to thrust loads that tend to push the gearbox shaft away from the gearbox or into the generator. Yet another feature is that the design lessens PV loads given the geometry constraints. 
         [0044]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.