Abstract:
A method and system for magnetically detecting thermal degradation of a component. A multiple of ferrous metal segments are attached to a component not within a lubrication circuit of a lubrication system with a thermally-affected bonding agent. The thermally-affected bonding agent is operable to detach at a threshold temperature at least one of the multiple of ferrous metal segments such that the at least one of the multiple of detached ferrous metal segments enters the lubrication circuit of the lubrication system. The at least one of the multiple of ferrous metal segments which detached are then detected within the lubrication system.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present disclosure claims the benefit of U.S. Provisional Patent Application No. 61/179,338, filed 18 May 2009. 
    
    
     BACKGROUND 
     The present disclosure relates to a system and method for failure detection. 
     Gearbox module failure detection is often provided by a magnetic chip detector. The detector collects magnetic particles caused by degradation of gear and bearing components within a gearbox housing and triggers a warning indicative of a potential failure. The detector operates in the presence of ferrous material such that when a single magnetic chip, or a collection of smaller chips suffices to bridge a gap in the magnetic chip detector completes an electrical circuit and a warning is triggered. 
     Sealed bearings typically have a grease lubricated bearing element with no active monitor. Over time, the sealed bearing may wear. This results in spalling debris which is contained within the sealed bearing by grease seals. As the spalling debris is contained within the sealed bearing, potential failure of the sealed bearing may be difficult to monitor even when the sealed bearing is located within a gear module which has a magnetic chip detector. 
     Periodic inspections of the sealed bearing for wear, excess play and binding may be manually performed. Although effective, such maintenance may be time consuming and require disassembly of the gear module. 
     SUMMARY 
     A method of magnetically detecting thermal degradation of a component according to an exemplary aspect of the present disclosure includes attaching a multiple of ferrous metal segments to a component not within a lubrication circuit of a lubrication system with a thermally-affected bonding agent. The thermally-affected bonding agent operable to detach at a threshold temperature at least one of the multiple of ferrous metal segments such that the at least one of the multiple of detached ferrous metal segments enters the lubrication circuit of the lubrication system. Detecting the at least one of the multiple of ferrous metal segments within the lubrication system. 
     An anti-torque system for a rotary wing aircraft according to an exemplary aspect of the present disclosure includes an outer ring of a sealed bearing and an inner ring of the sealed bearing. A bearing element between the outer ring and the inner ring. A multiple of ferrous metal segments bonded to the inner ring with a thermally-affected bonding agent, the thermally-affected bonding agent operable to break down at a temperature threshold and detach at least one of the multiple of ferrous metal segments from the inner ring. 
     A system according to an exemplary aspect of the present disclosure includes a lubrication system having a lubrication circuit. A component not within the lubrication circuit, the component having attached a multiple of ferrous metal segments with a thermally-affected bonding agent, the thermally-affected bonding agent operable to detach at a threshold temperature at least one of the multiple of ferrous metal segments such that the at least one of the multiple of detached ferrous metal segments enters the lubrication circuit of the lubrication system. A detector in communication with the lubrication system, the detector operable to detect the at least one of the multiple of ferrous metal segments which detach. 
     A rotary wing aircraft according to an exemplary aspect of the present disclosure includes a lubrication system having a lubrication circuit. A component not within the lubrication circuit, the component having attached a multiple of ferrous metal segments with a thermally-affected bonding agent, the thermally-affected bonding agent operable to detach at a threshold temperature at least one of the multiple of ferrous metal segments such that the at least one of the multiple of detached ferrous metal segments enters the lubrication circuit of the lubrication system. A detector in communication with the lubrication system, the detector operable to detect the at least one of the multiple of ferrous metal segments which detach. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1A  is a general perspective view of an exemplary rotary wing aircraft embodiment for use with the present invention; 
         FIG. 1B  is a schematic view of a drive system of a rotary-wing aircraft; 
         FIG. 1C  is a schematic view of a gear module; 
         FIG. 1D  is a sectional view of the gear module taken along line  1 D- 1 D of  FIG. 1C ; 
         FIG. 1E  is a schematic view illustrating a lubrication level within the gear module from a continual flow of lubrication from a lubrication system; 
         FIG. 2  is a sectional view of a sealed bearing assembly; 
         FIG. 3  is a perspective view of the sealed bearing assembly mounted within a pitch change shaft; 
         FIG. 4  is a schematic view of a non-limiting embodiment for magnetically detecting the thermal degradation of a component within a housing with a lubrication system; 
         FIG. 5  is a schematic view of another non-limiting embodiment for magnetically detecting the thermal degradation of a component within a housing with a lubrication system; and 
         FIG. 6  is a schematic view of another non-limiting embodiment for magnetically detecting the thermal degradation of a component within a housing with a lubrication system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  schematically illustrates an exemplary vertical takeoff and landing (VTOL) rotary-wing aircraft  10 . The aircraft  10  in the disclosed, non-limiting embodiment includes a main rotor system  12  supported by an airframe  14  having an extending tail  16  which mounts an anti-torque system  18 . The main rotor assembly  12  is driven about an axis of rotation A through a main rotor gearbox (MGB)  20  by a multi-engine powerplant system  22 —here having two engine packages ENG 1 , ENG 2  ( FIG. 1B ). The multi-engine powerplant system  22  generates the power available for flight operations and couples such power to the main rotor assembly  12  and the anti-torque system  18  through the MGB  20 . The main rotor system  12  includes a multiple of rotor blades  24  mounted to a rotor hub  26 . Although a particular helicopter configuration is illustrated and described in the disclosed embodiment, other configurations and/or machines, such as high speed compound rotary-wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors tilt-wing aircraft and non-aircraft applications such as wind turbines will also benefit herefrom. 
     Referring to  FIG. 1C , the anti-torque system  18  includes a gear module  18 T ( FIG. 1B ) driven by the MGB  20 . The gear module  18 T generally includes a housing  30  which receives a continual flow of lubrication from a lubrication system L (illustrated schematically). The housing  30  also communicates with a detection system D (illustrated schematically) such as a magnetic chip detector which operates to detect potential gearbox failure as generally understood. The detection system D includes a sensor S within the housing  30  typically below a level of lubricant thereon ( FIG. 1E ). The detection system may further communicate with a Health and Usage Monitoring system (HUMS) or other data logging system which is operable to communicate a warning to the aircrew and maintenance personnel. 
     Referring to  FIG. 1D , the gear module  18 T generally includes the housing  30 , a tail blade cuff assembly  32 , a tail rotor drive shaft  34 , a tail rotor pitch change shaft  36 , a drive gear  38 , a sealed bearing assembly  40  and a pitch change servo  42 . The drive gear  38  is supported upon bearings  44 A,  44 B for rotation about an axis of rotation B. The tail rotor drive shaft  34  is supported upon bearings  46 A,  46 B for rotation about an axis of rotation C. The drive gear  38  engages a shaft gear  48  to rotate the tail rotor drive shaft  34  and the attached blade cuff assembly  32 . 
     The tail rotor pitch change shaft  36  rotates with the tail rotor drive shaft  34  about the axis of rotation C, but serves no significant power transmission function. The tail rotor pitch change shaft  36  also slides along the axis of rotation C in response to actuation of the servo  42  to change the pitch of the tail blade cuff assembly  32  and the tail rotor blades attached thereto (not shown) and thus reduces or increases the thrust of the anti-torque system  18 . 
     Referring to  FIG. 1E , a continual flow of lubrication from the lubrication system L transits a lubrication circuit for communication with, for example only, each bearing  44 A,  44 B,  46 A,  46 B such that the lubricant is in fluid communication with the detection system D. Whereas the sealed bearing assembly  40  is a sealed bearing, any spalling debris is contained within the sealed bearing assembly  40  such that a potential failure of the sealed bearing assembly  40  may be difficult to monitor even though the sealed bearing assembly  40  is located within the housing  30  as the detection system D cannot directly identify a potential failure of the sealed bearing assembly  40 . 
     Referring to  FIG. 2 , the sealed bearing assembly  40  is mounted to the tail rotor pitch change shaft  36  (also illustrated in  FIG. 3 ) to accommodate relative rotation between the tail rotor pitch change shaft  36  and a rotationally fixed servo pushrod  42 P ( FIG. 1D ). The sealed bearing assembly  40  generally includes an outer ring  50 , an inner ring  52  and a bearing element  54  therebetween. The bearing element  54  may be a ball bearing, spherical bearing or other bearing arrangement which is greased and sealed within the outer ring  50  by seals  56 . The inner ring  52  defines a rod end  58  which connects with the servo pushrod  42 P. The sealed bearing assembly  40  may be manufactured of a steel alloy or a non-ferrous material. 
     The sealed bearing assembly  40  includes a plurality of ferrous metal segments  70  bonded to the inner ring  52  with a thermally-activated bonding agent which will release the segments  70  when a desired temperature is reached such that the segments  70  become detectable by the detection system D. It should be understood that thermally-activated bonding agents as utilized herein may include but are not limited to, adhesives, solders, glues, tapes and other agents including those formed onto the segments  70 . The desired temperature in the disclosed, non-limiting embodiment may be between 250-400 degrees F. (121-205 degrees Celsius). The segments  70  are sized so as to be small enough to be readily transported to the sensor S off the detection system D, but not so small as to be “burned off” with a fuzz burn feature typical of a magnetic chip detector. 
     The thermally-activated bonding agent may be selected so as to lose an amount of adhesion sufficient to release one or more segments  70  when a threshold temperature, e.g., indicative of imminent failure, is reached. As the component to which the segments  70  have been attached passes through the threshold temperature of the thermally-activated bonding agent, the segments  70  are released, pass through the lubrication system L, and are collected by the detection system D to generate an early signal that a bearing failure may be imminent. 
     Although bonded to the inner ring  52 , it should be understood that the ferrous metal segments  70  may be bonded in any desired manner to any component of the sealed bearing assembly  40 . The segments  70  may also be attached to any components not typically within the continual flow of lubrication but still likely to experience increased temperatures prior to a bearing failure such as components manufactured of ferrous and non-ferrous materials which include, but are not limited to, titanium, bronze, aluminum, nylon, composites, PEEK (PolyEtherEtherKetone) plastics, brass, magnesium, and combinations thereof. Furthermore, the ferrous metal segments  70  may alternatively or additionally be bonded to any surface of any gearbox component, part, or assembly of parts not typically within the continual flow of lubrication from the lubrication system but still likely to experience increased temperatures prior to a bearing failure. 
     The ferrous metal segments  70  may alternatively be provided with particular properties to facilitate specific identification from which component the segments  70  have detached. That is, sealed bearing assembly  40  may include one type of segments  70  which will provide one signal type to the detection system D, while another component may include segments of different properties which will provide a different signal type to the detection system  60 . The different properties may include, for example only, various ferrous concentrations which are specifically identifiable by the detection system D. Other properties may include the length, diameter, chemical composition, and color of the segments  70  amongst a plurality of assemblies within a single housing yet maintain uniformity amongst the segments  70  attached to any single component. In this manner, examination of the segments collected by the magnetic chip detector will facilitate the determination of which component may be experiencing temperatures in excess of the temperature threshold. 
     In one disclosed non-limiting embodiment, the sealed bearing assembly  40 , being sealed, is not within the continual flow of the lubrication system L lubrication circuit. The sealed bearing assembly  40  location within the housing  30 , however, allows for the debonded segments  70  to be readily communicated into the lubrication system L and thus into contact with the detection system D ( FIG. 4 ). Notably, the thermally-activated bonding agent will detach the segments  70  at a predefined temperature and the segments  70  essentially falls or are communicated from a “dry” section of the housing  30  which is not in the lubrication circuit of the lubrication system L into a “wet” section of the housing which is in the lubrication circuit of the lubrication system L and thus become “chips” identifiable by the detection system  60 . 
     Referring to  FIG. 5 , another disclosed non-limiting embodiment locates a sealed bearing assembly  40 A within the housing  30 A but in a position significantly remote from the lubrication system L. That is, no direct path is provided for the debonded segments  70  to essentially fall into the lubrication circuit of the lubrication system L. A guide  80 A within the housing  30 A that includes, but is not limited to, a tube, conduit, passage or other guide is positioned to capture the debonded segments  70  to transport the debonded segments  70  through the guide  80 A and into the lubrication system L for detection by the detection system D. 
     Referring to  FIG. 6 , another disclosed non-limiting embodiment locates a sealed bearing assembly  40 B external to the housing  30 B but in a position remote from the lubrication system L. Another guide  80 B is positioned to capture the debonded segments  70  external to the housing  30 B and transport the debonded segments  70  through the guide  80 B and into the housing  30 B to the lubrication system L for detection by the detection system D. 
     It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
     It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     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 disclosure. 
     The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.