Abstract:
An actuator system and a method for assembling the same are provided. An actuator system includes a housing and a cap. The housing includes a cavity defined by the housing and an opening defined in a wall of the housing. The housing encases an actuator within the cavity. The cap is coupled to the housing to facilitate shielding the opening from a surrounding environment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The embodiments described herein relate generally to aircraft landing gear systems and, more particularly, to electromechanical actuator systems used within aircraft landing gear systems. 
         [0002]    At least some known electromechanical actuator systems include a housing that experiences varying pressures and temperatures during a typical flight cycle of an aircraft. For example, during the aircraft ascent, the internal pressure and temperature within the housing decreases as the external pressure and temperature of the surrounding environment decrease until the aircraft is at cruising altitude. Conversely, during the aircraft descent, the internal pressure and temperature within the housing generally increases as the external pressure and temperature of the surrounding environment increases. 
         [0003]    At least some known electromechanical actuator systems balance the internal pressure and temperature within the housing with the external pressure and temperature of the surrounding environment by including an opening in the housing that facilitates venting of air into, and out of, the housing. For example, during aircraft ascent, the opening discharges air from the housing through the opening as the external pressure and temperature of the surrounding environment decreases. At cruising altitudes, the internal pressure and temperature within the housing are typically low enough that any liquid water within the housing may become frozen. During aircraft descent, air enters the housing through the opening as the external pressure and temperature of the surrounding environment increases. More specifically, when the landing gear bay doors open during landing, the warm, moist air may condense on an actuator mechanism encased within the housing when the actuator mechanism is still cold from the flight. Some condensation may be drawn into the actuator mechanism, and over time, such condensation may cause corrosion, hydrolysis, short circuits, and/or increase an overall mass of the actuator mechanism to the point wherein the actuator mechanism is inoperable. 
         [0004]    To address the condensation problem, at least some known electromechanical actuator systems hermetically seal the actuator mechanism within the housing and use desiccants to facilitate reducing an amount of condensation that can accumulate over an extended period of time. However, sealing the actuator mechanisms within the housing causes a substantial pressure difference to be created between the internal pressure within the housing and the external pressure of the surrounding environment. The increased pressure difference may induce additional strain on the seals of the housing, which may cause premature failure of the seals over time. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In one embodiment, a method for assembling an actuator system is provided. The method includes positioning a housing to encase an actuator within a cavity defined by the housing, and coupling a cap to the housing to facilitate shielding an opening defined in a wall of the housing from a surrounding environment. 
         [0006]    In another embodiment, an actuator system is provided. The actuator system includes a housing and a cap. The housing includes a cavity defined by the housing and an opening defined in a wall of the housing. The housing encases an actuator within the cavity. The cap is coupled to the housing to facilitate shielding the opening from a surrounding environment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional schematic illustration of an exemplary electromechanical actuator system that may be used on an aircraft; 
           [0008]      FIG. 2  is a cross-sectional schematic illustration of the electromechanical actuator system shown in  FIG. 1 ; 
           [0009]      FIG. 3  is a schematic illustration of an exemplary protective cap assembly used with the electromechanical actuator system shown in  FIG. 1 ; and 
           [0010]      FIG. 4  is a schematic illustration of the protective cap assembly shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    An electromechanical actuator system (EMA) includes a housing that maintains its aridity during a course of repeated flight cycles while reducing pressure differences that may be created between an internal pressure within the housing and an external pressure of the surrounding environment is desired. As described herein, maintaining the aridity of the housing facilitates increasing reliability of the actuator mechanism (actuator) encased within the housing, and reducing pressure differences facilitates reducing sealing requirements of the housing and increasing a useful seal life. 
         [0012]      FIG. 1  is a cross-sectional schematic illustration of an exemplary electromechanical actuator system, or EMA,  100  that may be used in an aircraft (not shown). In the exemplary embodiment, EMA  100  includes a moisture pump  110 , a protective cap  120 , a housing  130 , an actuator  140 , and a cavity  150 . Housing  130  includes a moisture pump  110 , which is an opening oriented from an internal surface to an external surface of housing  130 . Protective cap  120  is coupled to housing  130  such that it substantially covers moisture pump  110 . Actuator  140  is positioned within cavity  150  defined by the internal surface of housing  130 . 
         [0013]    During a typical flight cycle of the aircraft, housing  130  experiences varying internal pressures and temperatures. For example, during the aircraft ascent, the internal pressure and temperature within housing  130  decreases as the external pressure and temperature of the surrounding environment decrease until the aircraft is at cruising altitude. Conversely, during the aircraft descent, the internal pressure and temperature within housing  130  generally increases as the external pressure and temperature of the surrounding environment increases. 
         [0014]    To balance the internal pressure and temperature within housing  130  with the external pressure and temperature of the surrounding environment, moisture pump  110  facilitates venting of air into, and out of, housing  130 . For example, during aircraft ascent, moisture pump  110  discharges air from housing  130  through moisture pump  110  as the external pressure and temperature of the surrounding environment decreases. During aircraft descent, air enters housing  130  through moisture pump  110  as the external pressure and temperature of the surrounding environment increases. 
         [0015]    To protect actuator  140  from water, moisture, and/or condensation, protective cap  120  provides interfacial sealing that inhibits water from entering housing  130  through moisture pump  110 . More specifically, protective cap  120  facilitates protecting moisture pump  110  and actuator  140  from incidental water ingress, water spray, surface water, and clogging. Moreover, protective cap  120  prevents housing  130  from ingesting more liquid through moisture pump  110  than can be expelled from housing  130  through moisture pump  110 . In an alternative embodiment, protective cap  120  encases housing  130 . In such an embodiment, protective cap  120  provides moisture ingress protection due to its relative geometry and orientation to moisture pump  110 . 
         [0016]      FIG. 2  is a cross-sectional schematic illustration of EMA  100 . In the exemplary embodiment, housing  130  includes a moisture trap  210  and/or a desiccant cartridge  220 . Moisture trap  210  is a cavity that is defined between moisture pump  110  and cavity  150 . Desiccant cartridge  220  is a material positioned between moisture pump  110  and cavity  150 . 
         [0017]    In the exemplary embodiment, moisture trap  210  is sized and oriented to trap incidental liquid water ingress in a location remote from actuator  140 . More specifically, water seeping through moisture pump  110  is retained in moisture trap  210  and is prevented from contacting actuator  140 . Ultimately, any water residing in moisture trap  210  is expelled from housing  130  as air is channeled into and from housing  130  through moisture pump  110 . 
         [0018]    In the exemplary embodiment, desiccant cartridge  220  is fabricated from a material that enables it to absorb incidental liquid water ingress. More specifically, water seeping through moisture pump  110  is absorbed by desiccant cartridge  220  and is prevented from contacting actuator  140 . 
         [0019]      FIGS. 3 and 4  are schematic illustrations of an exemplary protective cap assembly  300  that may be used with EMA  100  (shown in  FIGS. 1 and 2 ). In the exemplary embodiment, protective cap assembly  300  includes protective cap  120 , a base  320 , a porous membrane  330 , an elastomer ring  340 , and a diffusion inhibition tube  350 . Elastomer ring  340  is also known as O-ring and is substantially circular. In alternative embodiments, each feature  120 ,  320 ,  330 ,  340 ,  350  can operate independently, or in any combination, of the other features. 
         [0020]    In the exemplary embodiment, protective cap assembly  300  is coupled to housing  130  such that it substantially covers moisture pump  110 . More specifically, housing  130  is coupled to base  320 , such that porous membrane  330  is retained against housing  130 . Moreover, housing  130  includes a groove  360  that is sized and oriented to position O-ring  340  between housing  130  and base  320 . More specifically, O-ring  340  is sized and shaped to fit securely in a mating relationship within groove  360  formed under base  320 . 
         [0021]    In the exemplary embodiment, porous membrane  330  inhibits water from entering housing  130  through moisture pump  110  while still enabling water to leave housing  130  through moisture pump  110  because of its composition. Porous membrane  330  can be fabricated from any material composition that facilitates this function. Some examples of porous membrane  330  include, but are not limited to, a fabric water barrier such as Teflon (Teflon is a registered trademark of the DuPont Company for products made from fluoropolymers), a sintered metal water barrier, and a sintered ceramic water barrier. 
         [0022]    In the exemplary embodiment, O-ring  340  is fabricated from an elastomer and has a substantially circular cross-section shape. Moreover, O-ring  340  facilitates sealing between housing  130  and base  320 . 
         [0023]    In the exemplary embodiment, diffusion inhibition tube  350  is a narrow tube that connects moisture pump  110  to cavity  150  (not shown in  FIGS. 3 and 4 ). Diffusion inhibition tube  350  slows water vapor ingress during steady state ground conditions. More specifically, diffusion inhibition tube  350  has a length that is sized relative to its diameter such that a length-to-diameter ratio of diffusion inhibition tube  350  facilitates reducing a rate of air exchange between the cavity of housing  130  and the surrounding environment. Thus, diffusion inhibition tube  350  facilitates reducing a rate of humidity exchange within housing  130 . 
         [0024]    Exemplary embodiments of a breather apparatus on electromechanical actuators for aircraft landing gear systems are described above in detail. The methods and systems are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other systems and methods, and are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications. 
         [0025]    Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
         [0026]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.