Abstract:
A bearing that includes a first bearing support member; a second bearing support member spaced from the first bearing support member, the first and second bearing support members each having a first end and a second end; and a resilient member between the first and second bearing support members, the resilient member having a radial thickness, the radial thickness varying between the first and second ends of the bearing support members, and whereby the bearing wears substantially constantly during its useful life.

Description:
FIELD OF THE INVENTION 
     The invention relates to a pitch bearing and more particularly the invention relates to a pitch bearing that includes a variable thickness resilient layer that produces bearing loading that promotes substantially constant bearing wear life. 
     BACKGROUND OF THE INVENTION 
     Helicopters include a rotor hub that is driven by a rotor shaft. A plurality of rotor blades are connected to the rotor hub, and each rotor blade is linked to the hub by a member frequently referred to by those skilled in the relevant art as either a pitch hinge or a pitch link. For purposes of this description the member shall be referred to as a pitch joint. Each pitch hinge is used to make adjustments to the pitch or angle of attack of the blades to control the amount of lift generated as the rotor blades are rotated by the rotor hub. Each pitch hinge includes a number of pitch bearings that support the pitch hinge when it experiences an applied shear force and moment as the rotor hub is rotated. 
     Turning now to the schematic representation of a conventional pitch hinge illustrated in FIG. 1, the pitch hinge  10  has an inner body  12  with an inboard end  14  where the pitch hinge connects to the rotor hub (not shown) and an outboard end  16  where the pitch hinge connects to the respective rotor blade (not shown). The pitch hinge body is enclosed by an outer housing  18  that directly connects the pitch hinge to the rotor hub and rotor blade assemblies. The housing is partially illustrated in FIG.  1  and the conventional means for connecting the housing to the rotor blade and to rotor hub are not illustrated. 
     A pitch hinge elastic center  20  is located between the inboard and outboard ends  14  and  16 . Conventional pitch bearings  22 ′ and  22 ″ are respectively located at the inboard and out board body ends and serve to support the pitch hinge as it experiences reactionary loading and applied rotational moments during use. For purposes of this disclosure, the elastic center of the pitch hinge is the location along the body of the pitch hinge where the reactionary loading forces produce no rotation. There is an applied moment at the elastic center. The location of the elastic center is dependent on a number of variables including the application environment for the pitch hinge, loading experienced by the pitch hinge and also the configuration and type of bearings used to support loading to the hinge. The moment applied about the elastic center is represented in FIG. 1 at the elastic center  20  by arrow  26 . 
     The inboard and outboard pitch bearings  22 ′ and  22 ″ are substantially similar and include inner annular bearing seat  28 ′ and  28 ″, outer annular bearing member  30 ′ and  30 ″ and annular resilient member  32 ′ and  32 ″ located between the inner and outer members. As shown in FIG. 1, the resilient member has a constant thickness as it extends axially along axis  25  between the inner and outer bearing members. The constant thickness is illustrated in the enlarged detail view FIG.  2  and is referred to in the Figure as “t”. Each pitch bearing  22 ′ and  22 ″ is seated on a respective sliding bearing surface  23  and  27 . During use, the bearing may be displaced in small axially directed distances along the sliding bearing surfaces. 
     When elastomeric bearings are loaded relative to elastic center  20  by applied moment  26 , an unbalanced load reaction and differential stress/strain occur in constant thickness resilient layers  32 ′ and  32 ″. As shown in the schematic representation of body  12  and bearings  22 ′ and  22 ″ in FIG. 3, the loading at outer bearing ends  35 A and  35 B is greater than the loading at inner bearing ends  36 A and  36 B. The different effective loads are represented schematically in FIG. 3 by differing the lengths of the tails of the load arrows. The greatest loads have the longest tails and the smallest loads have the shortest tails. As shown by the schematic representation of the reaction load distribution in FIG. 3, the load reaction (pressure distribution) increases in the axial direction along axis  25  from end  36 A,  36 B to end  35 A,  35 B as one moves farther away from the applied moment  26 . As a result, the inner and outer sleeves  28  and  30  will compress or pinch the elastomer layer  32  more at outer ends  35 A and  35 B than at the inner ends  36 A and  36 B. causing the outer portions of the bearing sleeves to wear out prematurely. The uneven load distribution provides uneven wear on the bearings and causes the outer portions of the bearing sleeves  23  and  27  to wear out prematurely. The portions of bearing surfaces  23  and  27  at ends  35 A and  35 B that experience the greatest loading wear out sooner than the portions of the bearing surfaces at ends  36 A and  36 B. 
     The elastomer portions at ends  36 A and  36 B wear out over period of use that is longer than the period it takes for elastomer portions at ends  35 A and  35 B to wear out. In order to maximize the useful life of the pitch bearings  22 ′ and  22 ″ it would be desireable to provide constant or even wear of the sliding bearing surface of each of the pitch bearings. 
     The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative pitch bearing is provided including features more fully disclosed hereinafter. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention this is accomplished by providing an elastomeric bearing which produces substantially constant bearing wear along the length of the sliding bearing surface. The bearing of the present invention comprises a bearing that includes a first bearing support member; a second bearing support member spaced from the first bearing support member, the first and second bearing support members each having a first end and a second end; and a resilient member between the first and second bearing support members, the resilient member having a thickness, the thickness varying between the first and second ends of the bearing support members, and whereby the bearing provides for constant bearing wear along the length of the bearing. The bearing may be a pitch bearing for use in a pitch hinge in a helicopter or may be used in an articulated vehicle. 
     In the bearing of the present invention the thickness of the resilient member varies linearly between the first and second bearing ends. Depending on the bearing loading the thicker end of the resilient member may be located at either the first or second bearing end. In the present invention bearing, the first bearing support member, the second bearing support member and the resilient member are annular and the thickness of the resilient member varies in the radial direction between the first and second ends. The first and second bearing support members have inner surfaces that are tapered inwardly and converge at the first end and the taper defines an angle that is between four and six degrees. 
     The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial longitudinal sectional view of a pitch hinge that includes prior art pitch bearings at the inboard and outboard ends of the pitch hinge; 
     FIG. 2 is an enlarged view of the portion of FIG. 1 enclosed by the dashed font circle identified as  2  in FIG. 1; 
     FIG. 3 is a schematic representation of conventional pitch bearings illustrating the unbalanced reaction loads at the inboard and outboard pitch bearings; 
     FIG. 4 is a partial longitudinal section view of a pitch hinge that includes the pitch bearings of the present invention at the inboard and outboard ends of the pitch hinge; 
     FIG. 5 is an enlarged view of the portion of FIG. 4 enclosed by the dashed font circle identified as  5  in FIG. 4; 
     FIG. 6 is a schematic representation of the pitch bearings of the present invention illustrating the balanced reaction loads at the inboard and outboard pitch bearings; 
     FIG. 7 is an enlarged view of the portion of FIG. 5 enclosed by the dashed font circle identified as  7  in FIG. 5; and 
     FIG. 8 is a schematic representation of the pitch bearings of the present invention illustrating an alternate orientation for the inboard and outboard pitch bearings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now turning to the drawing figures wherein like parts are referred to by the same numbers in the several views, FIGS. 4-8 illustrate the pitch bearing of the present invention included in pitch hinge  40 . The bearing of the present invention provides means for producing substantially constant bearing wear life along the length of the bearing. 
     It should be understood that although the pitch bearing of the present invention  42 ′ and  42 ″ is shown and described for use in a pitch hinge, the present invention may be used in a variety of suitable applications including the class of articulated vehicles comprising tractors, trucks earthmovers or the like. 
     The pitch hinge  40  includes many of the elements of prior art pitch hinge  10  previously described hereinabove in illustrated in FIGS. 1-3, including body  12  with axis  25 , and an elastic center  20  between the inboard and outboard ends  14  and  16  and a housing  18  that substantially encloses the body. Although the terms inboard and outboard are included in the reference names of body ends  14  and  16 , the ends  14  and  16  could also respectively be identified as “inner” and “outer” ends or “first” and “second” ends, and should not be limited to an application that includes inboard and outboard locations or directions. 
     Inboard and outboard bearing sleeves  41  and  43  are located along the body at the inboard and outboard body ends  14  and  16  and pitch bearings  42 ′ and  42 ″ of the present invention are seated on the respective bearing sleeves  41  and  43  that define sliding surfaces. The sleeves are shown in FIG.  4  and are similar to sleeves  23  and  27 . The bearings are substantially the same and include an annular first bearing support member or bearing seat  44 ′,  44 ″ in contact with the respective sleeve; an annular second bearing support member  46 ′,  46 ″ spaced from the first bearing support member radially outwardly along radial or lateral axis  45 ′, 45 ″ and a resilient member  48 ′,  48 ″ located between the first and second support members. See FIGS. 4 and 5. The housing  18  is supported by the second bearing support members  46 ′,  46 ″. 
     Because bearings  42 ′ and  42 ″ are substantially the same, for clarity purposes, as the description proceeds only bearing  42 ′ will be described. For reference purposes, when reviewing the drawing Figures, for elements that are included in the first and second bearings of the present invention in the first bearing  42 ′ the elements are identified by a reference number and a single prime and the equivalent element in the second bearing  42 ″ is identified using the same reference number used to identify the element in the first bearing along with a double prime marking adjacent the reference number. 
     The bearing support members  44 ′ and  46 ′ may be made from any suitable material however it is preferred that the members be made from stainless steel. The resilient member may also be made from any suitable resilient material however for purposes of describing the preferred embodiment of the invention the member  48 ′ is made from a natural rubber and is attached to the bearing support members  44 ′ and  46 ′ using a conventional adhesive such as CHEMLOK® Adhesive 250 supplied by Lord Corporation of Erie, Pa. 
     Each pitch bearing support member has a first end  49 ′ and a second end  50 ′. As shown in FIG. 5, the inner surfaces  52 ′ and  54 ′ of the first and second bearing support members diverge as the surfaces extend along axis  25  from the second end  50 ′ to the first end  49 ′. The slope or angle of taper is constant for each surface  52 ′,  54 ′ and the angle of taper is most preferably between 4° and 6°. This angle is identified as  56  in FIG.  7 . It should be understood that the bearing support member surfaces  52  and  54  may be given any suitable angle  56  and that the degree value of the angle is dependent on a number of variables including, but not limited to, the distance from the elastic center, the magnitude of the reactionary loading, the moment applied at the elastic center  20  and also the material comprising resilient member  48 . 
     FIG. 8 schematically illustrates an alternate bearing configuration. In the alternate configuration, the inner surfaces  52 ′ and  54 ′ converge as the surfaces extend along axis  25  from the second end  50 ′ to the first end  49 ′. 
     Although the resilient member  48 ′ as disclosed includes a constant or linearly slope surface  57 , if required, the member and also surfaces  52  and  54  may comprise non-linearly sloped surfaces. 
     Turning now to the resilient member  48 ′, as shown in FIGS. 4 and 5, the annular resilient member has a radial thickness that is variable between the ends of the bearing  49 ′ and  50 ′. As shown in FIGS. 4 and 5, radial dimension of resilient layer  48 ′ at end  49 ′ is greater than the radial dimension of the resilient layer at end  50 ′ along the direction of axis  45 ′ and in this way, the longitudinally extending member surfaces diverge in a linear manner between the ends  49 ′ and  50 ′. The bearing of the present invention  42 ′ that includes variable thickness layer  48 ′ provides constant bearing wear along the sleeves and bearing components and extends the useful life of the bearing  42 ′. 
     As shown in FIG. 6, when the portion of the member  48 ′ with the greatest radial dimension is located at end  49 ′, as the body is loaded and moment  26  is applied at the elastic center  20 , the reactionary load along the pitch bearings is substantially constant between ends  49 ′ and  50 ′. The evenly distributed reactionary load is represented by the arrows with tails that are substantially the same length. In this way, the pitch bearing resilient members will wear more constantly and evenly than prior art pitch bearings under similar loading conditions. As a result, it is expected that the pitch bearings of the present invention will have a longer useful life than prior art pitch bearings. This configuration of the resilient member is required when the axial forces are small and the shear loads and resultant moments are of larger magnitude. 
     Under alternative loading scenarios, it might be necessary to orient the resilient layer  48 ′ in the manner illustrated schematically in FIG. 8 with the portion of the member  48 ′ with the greatest radial dimension located at end  50 ′ and the portion of the member  48 ′ with the minimum radial dimension located at end  49 ′. This type of configuration is most useful when it is necessary to react to axial loads generally along axis  25 . Under such loading, the axial loads are greater than the applied moments and shear loads. 
     While I have illustrated and described a preferred embodiment of my invention, it is understood that this is capable of modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.