Abstract:
A ram air turbine assembly includes a spacer that controls axial movement of a bearing assembly supporting rotation of a driven shaft to limit compression of a bearing biasing member. A gearbox includes mating gears that transfer power through a strut to a generator. Bearings support rotation of the driven shaft and the biasing member generates a biasing load to maintain desired alignment between the mating gears. Axial thrust reversals generated during operation are prevented from fully compressing the biasing member by a spacer that defines a minimum compressed height and that further limits axial movement of the bearing assembly responsive to the thrust reversals of the driven shaft.

Description:
BACKGROUND 
     This disclosure generally relates to a gearbox for a ram air turbine assembly. More particularly, this disclosure relates to a bearing preload spring and spacer for supporting rotation of a gear shaft within a gearbox of a ram air turbine. 
     A ram air turbine (RAT) is a back up power generation device utilized in aircraft. The ram air turbine is deployed into airflow along the exterior of the aircraft and the turbine is driven by the airflow. The turbine may drive a generator, hydraulic pump or other power generation device. A strut or other extension member supports the turbine away from the aircraft. The generator or hydraulic pump may be supported within the RAT assembly and driven by a shaft extending from a gearbox driven by the turbine. During operation, a turbine may encounter cyclical loads that are in turn transmitted through the gearbox and corresponding gear interfaces. 
     SUMMARY 
     A disclosed ram air turbine assembly includes a spacer that controls axial movement of a bearing assembly supporting rotation of a driven shaft to limit compression of a bearing biasing member. A turbine drives a generator through a gearbox responsive to airflow. The gearbox includes mating gears that transfer power through a driveshaft to the generator. Bearings support rotation of the driven shaft and the biasing member generates a biasing load to maintain desired alignment between the mating gears and preload on the gear shaft bearings. Axial thrust reversals generated during operation are prevented from fully compressing the biasing member by a spacer that limits axial movement of the bearing assembly responsive to the thrust reversals of the driven shaft. 
     These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an example ram air turbine. 
         FIG. 2  is a cross sectional view of an example gearbox for a ram air turbine. 
         FIG. 3  is an enlarged sectional view of an upper bearing assembly for the example ram air turbine gearbox. 
         FIG. 4A  is a perspective view of an example spacer member. 
         FIG. 4B  is a cross sectional view of the example spacer member. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a ram air turbine  10  is generally indicated and is movable between a stowed position within an aircraft  12  and a deployed position shown. The ram air turbine  10  includes a turbine  14  with blades  16  that rotate responsive to air flow. The turbine  14  is suspended on a strut  18 . The strut  18  supports a gearbox  24  that transmits power from the turbine  14  to a generator  23  mounted within a generator housing  22 . The strut  18  is attached to the generator housing  22  that is pivotally attached to support member  20  of the aircraft  12 . 
     The disclosed example includes a generator  23 ; however the turbine  14  could also be utilized to drive a hydraulic pump or other power generation or conversion device. The ram air turbine  10  is moved to the deployed position shown such that airflow through the turbine blades  16  drive the turbine  14  which in turn drives a turbine shaft  26  ( FIG. 2 ) extending into gearbox  24 . The gearbox  24  in turn transmits power with a driveshaft up through strut  18  to drive the example generator  23 . 
     Referring to  FIG. 2 , the turbine shaft  26  is supported for rotation about an axis  17  by bearing assemblies  30 . The turbine shaft  26  supports a turbine gear  28 . In this example the turbine gear  28  is connected to the turbine shaft  26  using a keyway and drives a pinion gear  34  that is supported on a corresponding pinion shaft  32 . The example turbine gear  28  and pinion gear  34  are bevel gears that engage at an angle relative to the axis of rotation  17  of the turbine shaft  26  and axis  15  about which the pinion shaft  32  rotates. 
     The pinion shaft  32  extends upward from the gearbox  24  through the strut  18  to drive the generator within the generator housing  22  ( FIG. 1 ). The pinion shaft  32  is supported for rotation relative to the turbine shaft  26  within the gearbox  24  by a lower pinion bearing assembly  36  and an upper pinion bearing assembly  38 . 
     The upper and lower pinion bearing assemblies  38 ,  36  not only support rotation of the pinion shaft  32  but also control axial thrust generated during operation. The lower bearing assembly  36  and upper bearing assembly  38  control axial movement of the pinion shaft  32  and thereby the pinion gear  34  that may occur responsive to driving engagement between the turbine gear  28  and the pinion gear  34 . 
     Referring to  FIG. 3  with reference to  FIGS. 1 and 2 , the example upper bearing assembly  38  includes an inner race  40  that is pressed or fixed to the pinion shaft  32 . A set of balls  44  are supported between the inner race  40  and an outer race  42 . The upper bearing assembly  38  is supported within a retainer  46 . In this example, the retainer  46  is constructed of an aluminum material. Within the retainer  46  is disposed a liner  48 . The example liner  48  is fabricated from a stainless steel material to provide desired durability and wear characteristics. 
     Rotation of the pinion shaft  32  as driven by the turbine shaft  26  results in an axial thrust load along the axis  15  in the direction indicated by arrows  62  and  64 . Normal axial thrust is in the direction of arrow  62  towards a center point of engagement between turbine gear  28  and the pinion gear  34 . However, the torque loads between the turbine shaft  26  and the driving engagement of the pinion shaft  32  with the generator  23  can cause a reversal of the axial load on the pinion shaft  32  as is indicated by arrow  64 . A reversal in the axial loads on the pinion shaft  32  can cause misalignment between the pinion gear  34  and the turbine gear  28 . Misalignment in turn may cause increased wear of the meshing gear teeth of the turbine gear  28  and pinion gear  34 . 
     A biasing member is utilized that generates a biasing ‘preload’ force in the direction indicated by arrow  60 . The arrow  60  points in a direction generally toward a center point of the engagement interface between the turbine gear  28  and the pinion gear  34 . In this example, the biasing member comprises a wavy spring  52  that is disposed within an annular space  54  between a spacer  50  and the sleeve  48  disposed in the retainer  46 . The wavy spring  52  is disposed within the annular space  54  defined by the spacer  50 . As appreciated, although a wavy spring  52  is shown in this disclosed example, other biasing members such as coil springs, resilient material or other known biasing members. 
     The annular space  54  defined by the spacer  50  is defined by a lip  68  that extends axially from a shoulder  70 . The shoulder  70  defines a seat on which the wavy spring  52  exerts its biasing force downward onto the outer race  42  of the bearing assembly  38 . The lip  68  includes an inner surface  65  that defines a first inner diameter  74 . The spacer  50  includes a bottom surface  72  that is in direct abutting contact with a first surface  75  of the outer race  42  of the bearing assembly  38 . 
     The spacer  50  is disposed about the pinion shaft  32  with the lip  68  disposed on a radially innermost portion of the shoulder  70 . The lip  68  extends the axial distance  56  from the shoulder  70  ( FIG. 4B ) that is less than the overall axial width  88  ( FIG. 4B ) of the annular space defined within the retainer  46  such that a gap  58  allows some axial movement of the upper bearing assembly  38  and pinion shaft  32 . Reversal of axial thrust forces in the direction indicated by arrow  64  could flatten out the wavy spring  52 . However, the annular space  54  defined by the lip  68  of the spacer  50  prevents complete compression of the wavy spring  52 . Instead, the example lip  68  that extends the axial distance  56  from the shoulder  70  defines a maximum compression height allowable for the wavy spring  52 . The lip  68  will contact the sleeve  48  prior to the wavy spring  52  reaching a fully compressed or flattened state. The wavy spring  52  remains safely within the annular space  54  defined by the lip  68 . 
     The retainer  46  also includes an upper annular cavity  65  that houses a lip seal  66 . The lip seal  66  is biased against the outer surface of the rotating pinion shaft  32 . The lip seal  66  provides a desired seal to prevent lubricants from leaving the gearbox or other external contaminants from entering the gearbox and interfering with operation of the bearing assembly  38 . 
     Referring to  FIGS. 4A and 4B , the example disclosed spacer  50  is generally ring shaped and includes a first inner diameter  74  that extends to a second inner diameter  76  that is larger than the first inner diameter  74 . An angled surface  82  extends at an angle  86  between the first and second diameters  74  and  76 . The angle  86  in a non-limiting dimensional embodiment is provided in range between 60° and 70°. The bottom surface  72  is disposed radially outward from the second inner diameter  76  to an outer diameter  84 . 
     In a non-limiting dimensional embodiment the outer diameter  84  is provided within a range of 2.439 inches (61.95 mm) and 2.429 inches (61.70 mm) and the inner diameter  74  is provided in a range between 1.850 inches (46.99 mm) and 1.830 inches (46.48 mm). A ratio of the outer diameter  84  to the inner diameter  74  being between 1.31 and 1.33. 
     In a non-limiting dimensional embodiment, the inner diameter  76  is provided within a range of 2.205 inches (56.01 mm) and 2.25 inches (57.15 mm). A ratio between the outer diameter  84  and the inner diameter  76  is between 1.091 and 1.106. As appreciated, the example may be scaled in size to tailor the spacer configuration to application specific requirements. 
     The ratios between the outer diameter  84  and the two inner diameters  74  and  76  define the surface  72  that abuts the outer race of the  42 . Accordingly, the dimensions of the surface  72  provide the desired durability and wear properties of the spacer  50 . Moreover, the lip  68  is defined between the inner diameter  74  and an outer diameter  90 . In a non-limiting embodiment, the outer diameter  90  is defined within a range of 1.990 inches (50.55 mm) and 1.970 inches (50.04 mm) and is in concert with the inner diameter  74  defines the surface area of the lip  68  that contacts the retainer  46  in the event of a thrust reversal. In this disclosed example, a ratio of the outer diameter  90  to the inner diameter  74  is between 1.06 and 1.09. 
     The spacer  50  includes the shoulder  70  and the lip  68  that extends from the shoulder  70 . The lip  68  defines the axial distance  56  (Also see  FIG. 3 ). The axial distance  56  is determined relative to the biasing member, in this disclosed example the wavy spring  52 . The axial distance  56  is determined to provide a minimum compressed height of the wavy spring  52 . In other words, the maximum compression of the wavy spring  52  is attained only when the lip  68  comes into contact with the corresponding surface of the liner  48 . 
     The lip  68  is defined as the axial distance  56  from the shoulder  70  and is related to the overall width  88  of the spacer  50  to provide a desired space for the biasing member  52 . In one non-limiting embodiment the distance  56  is provided in a range between 0.072 inches (1.83 mm) and 0.082 inches (2.08 mm) and the overall width  88  is provided in a range between 0.180 inches (4.57 mm) and 0.170 inches (4.32 mm). A ratio of the total width  88  relative to the distance  56  being between 2.95 and 3.64. 
     The lip  68  limits and controls movement of the bearing assembly  38  in response to axial thrust reversal indicated by the arrow  64 . The biasing wavy spring  52  the bearing assembly  38  towards the center of the interface between the pinion gear  34  and the turbine gear  28 . However, when the axial thrust force indicated by  64  exceeds the biasing force of the wavy spring  52 , the spacer  50  and lip  68  prevent over compression of the wavy spring  52  in the interim until the axial thrust forces return to the direction indicated by arrow  62 . 
     Referring back to  FIG. 3  with continued reference to  FIG. 2 , the example bearing assembly  38  is a component part of a replaceable unit supported within the retainer  46 . The retainer  46  includes the liner  48  and the bearing assembly  38  including the inner outer races and the ball  44  disposed therebetween. The liner  48  is provided between the bearing assembly  38  and the inner surface of the retainer  46 . The liner  48  is provided in this example to provide a wear bearing surface that is more durable than the retainer assembly  46 . In this example, the retainer  46  is fabricated from an aluminum material for weight saving purposes. 
     The retainer  46  also defines an external groove  78  that supports a seal  80 . During maintenance operations the entire containment case  46  can be removed and replaced. Alternatively, the retainer  46  may be removed so that the wavy spring  52  and bearing assembly  38  may be replaced followed by reinstallation of the retainer  46  about the pinion shaft  32 . 
     As appreciated, although the example retainer  46  is fabricated from aluminum material, the example retainer  46  may also be fabricated from other material to relieve the need for the use of another part as is disclosed as the liner  48 . In such an instance, the retainer  46  would include dimensions that support and hold the bearing assembly  38  as desired. 
     Accordingly, the wavy spring  52  provides the desired bias on the bearing assembly  38  to counter thrust reversals and maintain a desired relative orientation between the pinion gear  34  and turbine gear  28 . Moreover, the example spacer  50  prevents over compression of the wavy spring  52  in a manner that provides an increase in durability. Additionally, the spacer  50  limits maximum movement of the bearing assembly  38  in response to possible thrust reversals during operation. 
     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 this disclosure. For that reason, the following claims should be studied to determine the scope and content of this invention.