Patent Abstract:
A lubrication system includes a reserve housing configured to retain a lubrication fluid. A supply line in fluid communication with the reserve housing is configured to provide pressurized lubrication fluid to the reserve housing. An overflow tube has an overflow port, the overflow tube being configured to prevent the volume of the lubrication fluid from exceeding a certain amount. A metering jet is configured to allow the lubrication fluid to flow from the reserve housing onto a component, such as a bearing, in the gearbox at a predetermined rate. The metering jet provides flow of the lubrication fluid onto the bearing even when the supply line no longer provides pressurized lubrication fluid to the reserve housing.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/469,838, filed 31 Mar. 2011, titled “Gearbox with Passive Lubrication System,” which is hereby incorporated by reference for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present application relates to a passive lubrication system that is configured to provide lubrication in a gearbox during a loss of lubrication event. 
     2. Description of Related Art 
     Typically, a rotorcraft gearbox is required to have the capability to operate for a specific period of time during which the primary lubrication pressure system has malfunctioned. One typical solution is for the gearbox lubrication system to include a primary lubrication system and a completely redundant lubrication system. The redundant lubrication system is activated upon failure of the primary lubrication system. Having a completely redundant lubrication system adds considerable weight, complexity, and cost to the rotorcraft. 
     Hence, there is a need for an improved gearbox lubrication system. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the system of the present application are set forth in the appended claims. However, the system itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic side view of a rotorcraft, according to an illustrative embodiment of the present application; 
         FIG. 2  is a partial schematic side view of the rotorcraft of  FIG. 1 , according to an illustrative embodiment of the present application; 
         FIG. 3  is a partial cross-sectional view of a gearbox, taken at section lines in  FIG. 2 , according to the preferred embodiment of the present application; 
         FIG. 4A  is a partial cross-sectional view of a gearbox, according to an alternative embodiment of the present application; and 
         FIG. 4B  is an enlarged view of a portion of the partial cross-sectional view of the gearbox from  FIG. 4A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. 
     The system of the present application includes a passive lubrication system that is configured to provide continual lubrication to gearbox components for a period of time during a “run dry” or emergency condition. A “run dry” condition can exist when the primary pressurized lubrication supply has been terminated through a system malfunction, battle damage, or the like. During the run dry scenario, the passive lubrication system of the present application provides continued lubrication to gearbox components without active command. 
     Referring to  FIGS. 1 and 2  in the drawings, a rotorcraft  101  is illustrated. Rotorcraft  101  has a rotor system  103  with a plurality of main rotor blades  111 . Rotorcraft  101  further includes a fuselage  105 , landing gear  107 , a tail member  109 , and tail rotor blades  113 . An engine  115  supplies torque to a main rotor mast  117  via a gearbox  327  for the rotating of main rotor blades  111 . Engine  115  also supplies torque to a tail rotor drive shaft  119  for the rotating of tail rotor blades  113 . The pitch of each main rotor blade  111  can be selectively controlled in order to selectively control direction, thrust, and lift of rotorcraft  101 . Further, the pitch of tail rotor blades  113  can be selectively controlled in order to selectively control yaw of rotorcraft  101 . Rotorcraft  101  is illustrated for exemplary purposes only. It should be appreciated that the system of the present application may be used on aircraft other than rotorcraft, such as airplanes, tilt rotors, unmanned aircraft, to name a few examples. Further, the system of the present application may be used on non-aircraft vehicles and implementations. 
     Referring now also to  FIG. 3 , a passive lubrication system  301  is illustrated in conjunction with gearbox  327 . In the illustrated embodiment, gearbox  327  is depicted as a gearbox on rotorcraft  101 ; however, it should be appreciated the system  301  may be equally implemented on a variety of vehicles and structures having gearboxes that require lubrication. Gearbox  327  functions to convert high speed rotation of an output drive shaft of engine  115  into low speed rotation of main rotor mast  117 . Gearbox  327  includes a plurality of gears and bearings that require lubrication to properly function. 
     Lubrication of gearbox  327  is essential to the operation of rotorcraft  101 . Rotorcraft regulatory agencies, such as the Federal Aviation Administration (FAA) may require that gearbox  327  be operable for a requisite period of time after the primary pressurized lubrication system has failed. Such a requirement in a rotorcraft gearbox may be referred to as “run dry” capability requirement. 
     System  301  includes a reserve housing  303  configured to contain a certain volume of lubrication fluid  321 . Reserve housing  303  is preferably cast or machined such that reserve housing  303  is a structural member capably of carrying loads. In such an embodiment, reserve housing  303  is integral with the gearbox housing such that the gearbox housing and the reserve housing  303  are a single cast or machined structure. Reserve housing  303  can alternatively be a separate unit from the gearbox housing, such that reserve housing  303  can be attached to the gearbox housing with one or more fasteners and seals, for example. A lubrication fluid supply line  323  provides pressured lubrication fluid to the interior of reserve housing  303  during normal operating conditions. Furthermore, the pressurized primary lubrication system that provides pressurized lubrication fluid to lubrication fluid supply line  323  can be configured to provide lubrication to the interior of the gearbox in other locations as well. 
     System  301  preferably further includes an overflow tube  305  having an overflow entry port  307 . Overflow tube  305  is at least partly configured to prevent the volume of lubrication fluid  321  within reserve housing  303  to exceed a predefined level dictated by the location of overflow entry port  307 . During normal operation, lubrication fluid supply line  323  continuously provides pressurized lubrication fluid  321  to the interior of housing  303 . As such, lubrication fluid  321  enters overflow entry port  307  and is gravity fed down through the interior of overflow tube  305  and through an overflow exit port  309 , along an overflow direction  311  into gearbox  327 . Overflow tube  305  can include a filter or screen for removing any undesired contamination from lubrication fluid  321 . Overflow tube  305  is preferably removable, via a fastener, in order to facilitate inspection and maintenance. One or more seals can be used to prevent leakage of lubrication fluid  321  between overflow tube  305  and reserve housing  303 . Overflow tube  305  is also configured to act as a vent to allow air to flow to/from the interior of reserve housing  303  to/from the interior of gearbox  327 . For example, air can flow through overflow tube  305  when supply line  323  fills reserve housing  303 . Similarly, air can flow into reserve housing  321  when lubrication fluid  321  drains out through metering jet  313  so as to prevent a vacuum from forming therein. 
     It should be appreciated that supply line  323  can include a check valve in order to prevent lubrication fluid  321  from flowing back down supply line  323 . In an alternative embodiment, supply line  323  is located on a side portion of reserve housing  103 , which can cause a check valve in supply line  323 , or other means of preventing reverse flow of lubrication fluid  321 , to be particularly desirable. 
     System  301  preferably also includes a metering jet  313 . In the illustrated embodiment, metering jet  313  includes a plurality of metering jet orifices  315 . Orifices  315  are configured to receive lubrication fluid  321 , which is gravity fed through a metering jet exit port  317 . Flow of lubrication fluid  321  is metered through metering jet  313  between orifices  315  and exit port  317  along a direction  319 , and onto a bearing  325 . Metering jet  313  preferably includes a filter or screen for removing any undesired contamination from lubrication fluid  321 . Metering jet  313  is preferably removable, via a fastener, in order to facilitate inspection and maintenance. One or more seals can be used to prevent leakage of lubrication fluid  321  between metering jet  313  and reserve housing  303 . 
     During a loss of lubrication situation, the lubrication supply from supply line  323  can cease to supply lubrication fluid  321  to housing  303 . Even though lubrication fluid  321  is not being pressure fed into housing  303 , system  301  is configured to continuously supply lubrication fluid  321  to bearing  325  until reserve housing  303  is emptied of lubrication fluid  321 . Reserve housing  303 , orifices  315 , and exit port  317  are all configured so the lubrication fluid  321  is metered and allowed to flow onto bearing  325  for a requisite period of time. For example, the requisite period of time may be thirty minutes. The requisite period of time allows the pilot of the rotorcraft to safely land while the gearbox  327  is operable. 
     System  301  is configured to be passive in that it operates to provide lubrication fluid  321  to bearing  325  during a loss of lubrication situation without requiring an affirmative command from separate entity, such as pilot or detection system. Further, system  301  is configured to passively provide lubrication fluid  321  to one or more bearings  325  for a period of time so as to satisfy a “run dry” requirement. 
     System  301  is also configured such that the lubrication fluid  321  in reserve housing  303  is continuously heated, circulated, and filtered during normal operating conditions. More specifically, normal operating conditions allow for the continuous introduction of lubrication fluid  321  into reserve housing  303  via supply line  323 , as well as the continuous flow of lubrication fluid  321  from reserve housing  303  into gearbox  327  through overflow exit port  309  and metering jet exit port  317 . The continual exchange of lubrication fluid  321  in reserve housing  303  insures that lubrication fluid  321  is in condition for use upon failure of the primary pressurized lubrication system. 
     Even though system  301  is illustrated as having only one overflow tube  305  and one metering jet  313 , it should be appreciated that system  301  may include a plurality of overflow tubes  305  and metering jets  313 . For example, each metering jet  313  may be strategically located above critical bearings which need lubrication fluid  321  for operation of gearbox  327 . It should be appreciated that the bearings receiving lubrication fluid  321  via metering jet  313  may also be gears, or any other type of moving part that may require lubrication to minimize friction. 
     Referring now also to  FIGS. 4A and 4B  in the drawings. As shown in  FIG. 4A  the reserve housing  303  is a separate unit from the gearbox housing. As shown in  FIG. 4B  the metering jet  313  preferably includes a filter or screen for removing any undesired contamination from lubrication fluid  321 . 
     The passive lubrication system  301  provides significant advantages, including: 1) passively lubricating the gearbox during a failure of a primary pressurized lubrication system; and 2) providing heated, filtered, and circulated lubrication fluid that is available during the failure of a primary pressurized lubrication system. 
     It is apparent that a system with significant advantages has been described and illustrated. Although the system of the present application is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.

Technology Classification (CPC): 5