Abstract:
An example ram air turbine generator assembly includes a generator housing that holds a generator in axial alignment with a hydraulic pump. The generator housing includes a wall having contacting portions that contact a stator of the generator and spaced portions that are radially spaced from the stator. The generator wall is designed to be strong enough to withstand HLSD and windmilling vibrations, while flexible enough to accommodate thermal expansion.

Description:
BACKGROUND 
       [0001]    This disclosure relates to ram air turbines utilized to provide electric and hydraulic power to an aircraft. More particularly, this disclosure relates to a housing of a ram air turbine generator. 
         [0002]    A ram air turbine is used to generate supplemental power in an aircraft by extracting power from an air stream along the exterior of the aircraft during flight. The ram air turbine includes a turbine that drives an electric motor and/or hydraulic pump. In operation, the turbine is moved from a stowed position within the aircraft to a deployed position just outside of the aircraft such that the blades of the turbine are in the air stream and also have an operating clearance with the aircraft. The turbine is mounted at the end of a strut and drives a turbine drive shaft that in turn drives the electric motor and/or hydraulic pump. 
         [0003]    The ram air turbine may experience extreme loads, such as during high level, short duration events (HLSDs). During an aircraft engine blade loss event, the severe HLSD vibrations occur first as the engine spools down. Then, as it continues to turn due to air loads, a high unbalance load continues to drive the longer duration windmilling vibrations. Either or both of these vibrations could significantly reduce the fatigue life of RAT components. 
         [0004]    As known, windmilling is generally unpowered aircraft engine rotation that occurs at frequencies below most RAT resonant frequencies. However, HLSD is high level resonant vibration wherein one or more RAT modes are excited to resonance as the engine spools down and this causes high loads through the RAT housings. As the aircraft engine speed drops, the excitation frequency seen by the RAT sweeps from high to low frequencies, passing through normal RAT resonance frequencies on the way down. Thus it is not generally possible to design a RAT with natural frequencies that avoid a HLSD sweep event. Strengthen the RAT helps the RAT to endure the event. Also, the duration of spool down time is a fraction of the windmilling duration and so the number of fatigue cycles for HLSD is relatively small. Consequently, a practical design of the load bearing housings is feasible with appropriate load paths and careful attention to minimizing stress concentrations 
         [0005]    A generator housing of the ram air turbine needs to withstand these loads while accommodating changes in part dimensions due to thermal variations. 
       SUMMARY 
       [0006]    An example ram air turbine generator assembly includes a generator housing that holds a generator in axial alignment with a hydraulic pump. The generator housing includes a wall having contacting portions that contact a stator of the generator and spaced portions that are radially spaced from the stator. 
         [0007]    Another example ram air turbine generator housing assembly includes a wall having a portion extending axially along the length of a generator stator. The wall swivels with the generator between a stowed position and a deployed position about pivot. Portions of the wall that are vertically aligned with the pivot when the generator is in the stowed position are radially thickened relative to other portions of the wall. 
         [0008]    Yet another example ram air turbine generator assembly includes a generator housing having a wall. The wall has contacting portions that contact a stator of the generator and spaced portions that are radially spaced from the stator. At least 68% of the contacting portions and the spaced portions have a common radial thickness. A ratio of the common radial wall thickness to a diameter of the stator is from 0.018 to 0.022. 
         [0009]    An example method of installing a generator stator within a generator housing includes thermally fitting a generator stator within a generator housing. The wall of the generator housing extends axially along the length of the generator stator. The wall has contacting portions that contact a generator stator of the generator and spaced portions that are radially spaced from the generator stator. At least 68% of the contacting portions and the spaced portions have a common radial wall thickness. A ratio of the common radial wall thickness to a diameter of the generator stator is from 0.018 to 0.022. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0010]    The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows: 
           [0011]      FIG. 1  is a schematic view of an example ram air turbine including a generator and a hydraulic pump. 
           [0012]      FIG. 2  is a sectional view of the  FIG. 1  ram air turbine. 
           [0013]      FIG. 3  is a section view at line  3 - 3  in  FIG. 2 . 
           [0014]      FIG. 4  is a perspective view of an example generator housing of the  FIG. 1  ram air turbine. 
           [0015]      FIG. 5  is another perspective view of the example generator housing of the  FIG. 1  ram air turbine. 
           [0016]      FIG. 6  is yet another perspective view of the example generator housing of the  FIG. 1  ram air turbine. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIGS. 1 and 2 , an example ram air turbine assembly (RAT)  10  is mounted to an airframe  12  and is deployable to provide both electric power and hydraulic power. The example RAT  10  includes a turbine  14  that rotates responsive to air flow along the outside of the airframe  12 . The turbine  14  is supported at the end of strut  22  attached to a generator housing  24 . The generator housing  24  is mounted for rotation to the airframe  12  with a swivel post pivot  28 , which functions as a pivot for the housing  24 . 
         [0018]    A ram air turbine generator assembly  18  includes a generator rotor  32 , a generator stator  34 , and the generator housing  24 . During assembly, the generator rotor  32  and the generator stator  34  are placed within the housing  24 . In one example, the generator stator  34  is press-fit within the generator housing  24 . 
         [0019]    The generator rotor  32  is coupled to a hydraulic pump  38 . The generator rotor  32  is rotated relative to a stator  34  to generate electric power that can be supplied to an aircraft system, such as is schematically indicated at  40 . The hydraulic pump  38  receives fluid from a fluid supply  44  and pumps the fluid to various systems indicated at  42  that utilize pressurized fluid for operation. The generator assembly  18  and the hydraulic pump  38  are axially aligned. The rotating portions of the generator assembly  18  and the hydraulic pump  38  rotate about a common axis  54 . 
         [0020]    The turbine  14  rotates to drive a turbine driveshaft  46  about an axis  48 . The turbine driveshaft  46  drives a gearbox  50 . The example gearbox  50  is disposed aft of the turbine  14  and along the axis  48  of rotation of the turbine  14  and turbine driveshaft  46 . The example gearbox  50  drives a torque tube  52  that rotates about the axis  54 , which is transverse to the axis  48 . The torque tube  52  extends from the gearbox  50  through the strut  22  to the generator rotor  32 . The torque tube  52  is coupled to the generator rotor  32 . 
         [0021]    The example gearbox  50  includes gears that provide a desired ratio of rotational speed between the turbine driveshaft  46  and the torque tube  52 . In this example, the torque tube  52  is rotated at a greater speed than the turbine driveshaft  46 . The gearbox  50  can be configured to provide any desired speed ratio relative to rotation of the turbine  14 . 
         [0022]    The speed at which the torque tube  52  is rotated is determined to provide the desired rotational speed required to drive the generator rotor  32  and produce a desired amount of electrical energy at the desired frequency. The electrical energy produced by the generator is then transmitted to the aircraft system schematically indicated at  40 . 
         [0023]    A second drive shaft  56  couples the hydraulic pump  38  in rotation with the generator rotor  32  such that the hydraulic pump  38  rotates at the same speed as the generator rotor  32 . As the hydraulic pump  38  and the generator rotor  32  are coupled to rotate together, the hydraulic pump  20  communicates pressurized fluid to the aircraft systems  30  at the same time as the generator produces electric power. The hydraulic pump  38  and the generator  18  may supply power together or separately. 
         [0024]    The generator housing  24  includes a mounting bracket  60  and an integral swivel bracket  58 . The mounting bracket  60  attaches to an actuator  62 . The actuator  62  drives movement of the RAT  10  between a stowed position within the airframe  12  and the deployed position schematically shown in  FIG. 1 . 
         [0025]    The swivel bracket  58  mounts to the swivel post pivot  28  to support the RAT  10 . The strut  22  is attached to the generator housing  24  and therefore moves with the pivoting movement of the generator housing  24 . The hydraulic pump  38  is mounted to the generator housing  24  and therefore also rotates with the generator housing  24  during movement to and from the deployed position. 
         [0026]    Referring to  FIGS. 3 to 6 , the housing  24  includes a wall  64  that extends circumferentially about the axis  54 . The wall  64  provides a cavity  66  that receives the rotor  32  and the stator  34 . Notably, the wall  64  does not directly contact the entire outer circumference of the stator  34 . The wall  64  includes some contacting portions  68  and some spaced portions  72 . The contacting portions  68  directly contact the stator  34 , and the spaced portions  72  are radially spaced out from the stator  34 . In this example, the wall  64  includes six contacting portions  68  circumferentially alternating with six spaced portions  72 . 
         [0027]    Notably, throughout most of the housing  24 , the contacting portions  68  and the spaced portions  72  have approximately the same radial thickness t. In this example, the spaced portions  72  have a thickness t of 0.121 inches (3.073 millimeters) and the contacting portions  68  have a thickness of 0.135 inches (3.429 millimeters). The average thickness is 0.128 inches (3.251 millimeters). The spaced portions  72  are 90% of the thickness of the contacting portions  68 . In another example, both portions are 0.128 inches (3.251 millimeters) thick. The 0.128 inches (3.251 millimeters) average thickness could vary by +/−10% to achieve a desired ratio. For example, at  0 . 115  inches (2.921 millimeters) thickness, the ratio is 0.115/6.398=0.18 min. At 0.141 inches (3.581 millimeters) thickness, the ratio is 0.141/6.398=0.22. 
         [0028]    In this example, at an axial cross-section of the wall  64  that is perpendicular to the axis  54  (generally shown in  FIG. 3 ), at least 68% of the sectioned contacting portions and the sectioned spaced portions have a common radial thickness. Thus, the average thickness t of the wall  64  is generally the same about the circumference of the wall  64 . In one example, the thickness is about from 0.115 to 0.141 inches (2.92 to 3.58 millimeters). 
         [0029]    In this example, the stator  34  has an outer diameter d, and a ratio of the common radial thickness to the diameter d of the stator  34  is from 0.018 to 0.022. Also, in this example, the outer diameter d of the stator  34  is 6.405 inches (162.687 millimeters) and the outer diameter at the generator housing in this section is 7.62 inches (193.548 millimeters). 
         [0030]    Transition portions  76  extend from the contacting portions  68  to the spaced portions  72  so that the wall  64  is continuous about the entire stator  34 . Generally, in the section view of  FIG. 3 , the transition portions  76  have a radial and a circumferential component, and the contacting portions  68  and the spaced portions  72  lack a change in radial component. 
         [0031]    Fluctuating ambient temperatures and thermal energy levels may cause the wall  64  and the stator  34  to expand or contract relative to each other. Providing the contacting portions  68 , the spaced portions  72 , and the transition portions  76  enables wall  64  to flex and accommodate these thermal stress variations, while still providing support sufficient for withstanding high level short duration and windmilling vibrations in the stowed configuration. The wall thickness of transition portions  72  is approximately the same as the contacting portions  68  to maintain appropriate circumferential flexibility. 
         [0032]    The radial gap between the spaced portions  72  and the stator  34  function as axially extending channels  78 . The spaced portions  72  provide the outer boundary of the channels  78 . The channels  78  are used to duct flow air axially along the circumference of the stator  34 . The flow of air removes thermal energy from the generator assembly  18  to cool the generator assembly  18 . The hot air is outlet through slots ( 101 ) cut out on the top face ( 102 ) of the generator housing  24 . Additional vent holes ( 103 ) are provided at the base of the side walls of the mounting pedestal ( 104 ) for the pump housing. 
         [0033]    The example wall  64  extends axially at least the axial length of the stator  34 . In some examples, the axial length of the stator  34  is l s , and the axial length of the wall  64  is l w , which is greater than l s . In this example, the axial length of the main stator  34  is 3.725 inches (94.6 millimeters). The axial length of the wall of the generator housing is 5.88 inches (149.4 millimeters). The thickness of the splitline is 0.862 inches (21.9 millimeters). 
         [0034]    As seen in  FIG. 5 , a strong, stiff load path is required at location  80  between the strut and the actuator attachment lug. This area forms an anchoring feature to the circumferential ring around the stator. Since it only occurs at one location on the circumferential ring, it does not restrict the flexibility of the circumferential ring to expand as needed for thermal expansion. The location  80 , in this example, extends circumferentially about 9% of a circumference of the wall  64 . 
         [0035]    Since the thickness of the wall  64  is generally consistent about the axis  54 , the wall  64  includes divots  84  at the circumferential locations of the contacting portions  68 . The divots  84  reflect the differences between the radial locations of the contacting portions  68  and the spaced portions  72 . As appreciated, if the wall  64  did not include the divots  84 , the thickness of the wall  64  would increase in the areas of the contacting portions  68  relative to the spaced portions  72 . The divots  84  thus aid in an uniform hoop-type expansion of the wall  64  and also as material reduction feature. 
         [0036]    The example transition portions  76  include relatively large radii. In one example, an outer radius  90  of one of the transition portions  76  is about 0.520 inches (13.2 millimeters). 
         [0037]    To facilitate the housing  24  accommodating high level short duration loading and other types of loads, the example housing  24  is strengthened in selected areas. For example, although the thickness of the wall  64  is relatively consistent, the radially thickness is increased in areas  86  and  88  to some amount greater than t. The areas  86  and  88  are considered lateral stiffening ribs in the load path from the strut to pivot post  28 . 
         [0038]    If the turbine  14  is considered to extend from the axis  54  at a 12:00 position, the areas  86  and  88  are located at 4:30 and a 7:30 positions, respectively. The areas  86  and  88  extend circumferentially a distance C 86  and C 88 . In one example, these distances each represent about 15 degrees each of the 360 degree circumference of the wall  64 . 
         [0039]    When the example generator assembly  18  is in a stowed position, the areas  86  and  88  are vertically aligned with the swivel post pivot  28 . The areas  86  and  88  are also said to be in a common plane with the swivel post pivot  28 . Vertical, in this example, refers to the typical position of the stowed generator assembly  18  when on the ground or in straight or level flight. The areas  86  and  88  are thus in the load path extending from the strut interface back to the swivel post pivot  28 . 
         [0040]    The example housing  24  includes other features contributing to a high strength, low weight design resistant to high vibration level. For example, additional material may be added to the areas of the housing  24  at or near the swivel bracket  58  (see  FIG. 4 ). The housing  24  may also include a large sweeping radius in the area of the swivel bracket  58 . 
         [0041]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.