Abstract:
A lubrication system includes an additive and a delivery system. During normal operational conditions, the lubricating oil circulating in the transmission system is collected and contained in a secondary oil reservoir to retain a quantity of the lubricating oil for use in an oil-out condition. When an oil-out condition is detected, the additive is injected and mixed with the collected lubricating oil in the secondary oil reservoir or dispersed directly into a power transmission gearbox housing to enhance the characteristics of the lubricating oil and increases the operational time period of the power transmission gearbox during an oil-out condition.

Description:
[0001]     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/756,917, filed Jan. 5, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a lubrication system, and more particularly to a secondary lubrication system that incorporates a concentrated lubricating oil additive selectively injected into the secondary lubrication system to enable prolonged oil-out operation.  
         [0003]     Rotary-wing aircraft power transmission systems incorporate a multitude of gears and bearings which are subject to heat, sliding and surface wear. Such conditions are significantly increased during oil-out operating conditions caused by, for example, ballistic damage, pump failure and system leaks. The primary components of a power transmission system which may be failure points under oil-out conditions include bearings and gears which are constantly oil lubricated under normal conditions using pressurized oil jets or splash oil lubrication methods.  
         [0004]     The United States Department of Defense (U.S. DoD) currently imposes a requirement that all rotary-wing aircraft power transmission systems operate for a predetermined period of time in an oil-out condition. The requirement includes the capability to maintain flight operations for 30 to 60 minutes during the oil-out condition, albeit at reduced power levels, sufficient only to sustain level flight operations.  
         [0005]     Various emergency or secondary lubrication systems are known and practiced. Lubricating wicks and jets have been provided for lubricating individual components along with a small recirculation system. Air aspirated nozzles have also been utilized for delivering a stream of oil to each individual component. Even through relatively effective, these existing systems have not completely satisfies the U.S. DoD imposed requirements.  
         [0006]     Accordingly, it is desirable to provide a secondary or emergency lubrication system which allows a power transmission system to operate for a prolonged time period under oil-out conditions.  
       SUMMARY OF THE INVENTION  
       [0007]     The lubrication system according to the present invention includes a lubricating oil additive and a delivery system. During normal operational conditions, the lubrication oil which circulates in the transmission system is collected in a secondary or “emergency” oil reservoir for use in an oil-out condition. When an oil-out condition is detected, an additive is injected and mixed with the collected lubricating oil in the secondary oil reservoir or dispersed directly into a transmission gearbox housing. Upon mixing with the lubricating oil, the additive enhances the characteristics of the lubricating oil to enhance prolonged oil-out operation. Alternatively, on the detection of an oil-out situation, an auxiliary oil supply comprising a lubricant that contains additives for enhanced survival would be activated to inject the enhanced lubricant directly into a transmission gearbox housing.  
         [0008]     The lubrication system provides a typical power transmission system more than double the time period under which the transmission system may otherwise operate under an oil-out condition. Moreover, the lubrication system is capable of satisfying the U.S DoD imposed requirements for all areas/components within the power transmission system.  
         [0009]     The present invention therefore provides a secondary or emergency lubrication system which allows the power transmission system to operate for a prolonged time period under oil-out conditions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0011]      FIG. 1  is a general perspective view an exemplary rotary wing aircraft embodiment for use with the present invention;  
         [0012]      FIGS. 2A and 2B  are block diagrams of a lubrication system according to the present invention;  
         [0013]      FIG. 3  is a schematic diagram of a drip type of lubricating oil delivery system; and  
         [0014]      FIG. 4  is a schematic diagram of a mist type of lubricating oil delivery system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]      FIG. 1  schematically illustrates a rotary-wing aircraft  10  having a main rotor system  12 . The aircraft  10  includes an airframe  14  having an extending tail  16  which mounts a tail rotor system  18 , such as an anti-torque system. The main rotor assembly  12  is driven through a main power transmission gearbox (illustrated schematically at  20 ) by one or more engines E. Although a particular helicopter configuration is illustrated and described in the disclosed embodiment, other configurations and/or machines, such as ground vehicles, jet aircraft, turbofan engines, high speed compound rotary wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors and tilt-wing aircraft, will also benefit from the present invention.  
         [0016]     The main power transmission gearbox  20  carries torque from the engines E through a multitude of gear train paths to a main rotor shaft  22  of the main rotor system  12 . The gearbox  20  is preferably located within a housing  24  which may at least partially support the main rotor shaft  22 . The invention described herein is best illustrated by reference to the illustrated rotary-wing aircraft main power transmission gearbox having highly-loaded torque transmitting gears and bearings, however, it will be appreciated that the inventive teachings are applicable to any system which may require oil-out operation.  
         [0017]     Referring to  FIG. 2A , a lubrication system  26  communicates with the gearbox  20  within the housing  24 . The lubrication system  26  generally includes a primary oil reservoir  28  and an “emergency” or secondary oil reservoir  30  which retains a quantity of lubricating oil for use under “emergency” conditions such as an oil-out condition. Various primary communication systems  32  such as pumps and the like are utilized to circulate lubricating oil from the primary oil reservoir  28  into the housing  24  and to other high friction locations to provide for effective operation of the gearbox  20  and other system during normal operational conditions. The primary communication systems  32  need not be described in detail herein as various systems may be utilized in accordance with the principles of the present invention. Furthermore, it should be understood that various lubricating oils may also be used herewith, such as, for example, DOD-L-85734 or MIL-PRF-23699.  
         [0018]     Preferably, a quantity of lubricating oil contained within the secondary oil reservoir  30  is interchanged with operating lubricating oil during normal operational conditions of the lubricating system  26 . That is, the lubricating oil may be circulated through the secondary oil reservoir  30  such that the lubricating oil contained therein is refreshed yet always maintained in an essentially filled condition during normal operational conditions. Although the secondary oil reservoir  30  is illustrated within the housing  24 , it should be understood that other locations outside or partially inside and outside of the housing  24  may also be utilized with the present invention.  
         [0019]     Various secondary communication systems  34  such as a drip tank system  36  ( FIG. 3 ), an oil mist system  38  ( FIG. 4 ) as well as other “emergency” delivery systems are utilized to communicate the quantity of lubricating oil contained within the secondary oil reservoir  30  into the housing  24  and to other high friction locations to provide for short term operation of the gearbox  20  and other system during oil-out conditions. It should be understood that the secondary communication system  34  may be of various forms and may be integrated or separate from primary communication system  32 .  
         [0020]     An additive reservoir  40  contains an additive which is selectively injectable into the secondary oil reservoir  30  by a delivery system  42  to enhance the characteristics of the lubricating oil collected in the secondary oil reservoir  30  in response to an oil-out condition. The delivery system  42  communicates the additive from the additive reservoir  40  into the secondary oil reservoir  30 . Preferably, the delivery system  42  includes a pressurization system which injects and mixes the additive into the lubricating oil collected in the secondary oil reservoir  30  prior to communication into the housing  24 . Alternatively, the oil additive substance is not stored separately, but contained within the secondary oil reservoir  30  but only mixed with the collected lubricating oil during oil-out operation.  
         [0021]     Alternatively or in addition thereto, a delivery system  42 A ( FIG. 2B ) communicates the additive from the additive reservoir  40  directly into the housing  24 . The delivery system  42 A releases the additive into the atmosphere of the housing  24  separately from the lubricating oil delivered from the secondary oil reservoir  30 . The injection of the additive into the housing  24  essentially coats the entire interior contents of the gearbox  20  to enhance the functional surfaces of the bearings and gears therein. The delivery system  42 A may be pressurized by relatively small lightweight pressure canisters or may be attached to a remote air pressure device such as a bleed air source.  
         [0022]     The delivery system  42 ,  42 A additionally includes either or both of an automatic or manual control system  44  to control injection of the additive. That is, the lubrication system  26 ,  26 A may include either or both of an automatic check system such as an electromechanical system utilizing pressure monitoring sensors and/or require the involvement of a pilot operation manual initiator in the decision loop to initiate operation of the delivery system  42 ,  42 A to minimize a false detection of an emergency oil-out condition. This is preferred because the additive may have long term corrosive or other detrimental effects on the gearbox  20  due to the chemical aggressiveness of the additives.  
         [0023]     A wide variety of additives may be utilized. Preferably, however, the additive is selected based upon elemental testing and demonstrated performance in the areas of reduced friction, reduced heat generation, film forming capability, and chemical interaction with the gears and bearings. More preferably, the additive includes high concentrations of anti-wear (AW) and extreme-pressure (EP) compositions. Typically, phosphates are used as AW and EP additives. Specific additives may be selected according to their activation temperature and other characteristics. The additive also may preferably form, through a reaction of the nascent or oxidized moving component surface, a protective film on the surface thereof.  
         [0024]     Alternatively, the additive need not necessarily be lubricious but only have desirable characteristics such as: an appropriate melting or vaporization temperature; high specific heat (heat capacity); and/or high latent heat of fusion or vaporization. During an oil-out condition, temperature control may be more important than lubrication, although both of these factors are important and somewhat interdependent. To achieve improved wetting (coverage) of the moving component surface and thereby increase moving component cooling, especially in the possible presence of residual lubricating oil, a non-polar liquid assists with miscibility of the lubricant. Alternatively, while being a polar liquid, water is also a candidate whose thermal properties meet the requirements and whose polarity can be modified by the addition of certain soaps or other substances that possess both polar and non-polar characteristics.  
         [0025]     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.  
         [0026]     The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.