Abstract:
A self-aligning dynamic hinge sleeve for attachment to a pitch hinge in a position that places the hinge sleeve in contact with a pitch bearing. The hinge sleeve is comprised of an inner race, a middle race and an outer race, wherein the middle race is an elastomeric material, or another soft material, that bonds the inner and outer races together and allows the inner race and outer race to rotate with respect to each other. As the pitch hinge transmits forces and moment to a pitch shaft, the dynamic hinge sleeve aligns with a pitch bearing secured onto the pitch shaft. This results in a self-aligning pitch bearing rotor that significantly reduces the level of peak that loads upon a bearing and thereby permits the use of self-lubricating bearings in a rotor.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This invention was made with Government support under Contract No. DAAH01-99-3-R001. The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to dynamic hinge sleeves and more particularly to a self-aligning dynamic hinge sleeve for self-lubricated hinge bearings. 
     BACKGROUND OF THE INVENTION 
     Oil bearings and solid steel hinge sleeves are components of some typical rotors, including helicopter blade rotors. One drawback of this type of rotor is the cost of frequent scheduled and unscheduled maintenance and/or repairs. Moreover, a large percentage of rotorcraft ground time and maintenance expense is due specifically to difficulties with oil bearings, including oil leakage and bearing replacement. Thus, there exists a need for a rotor that requires less maintenance and thereby decreases costs. 
     One proposed solution to this problem is to replace the oil bearings with self-lubricated dynamic hinge bearings. The self-lubricated bearings are processed with long lasting, dry lubricant. These self-lubricated bearings require less unscheduled maintenance than oil bearings, which results in a lower life-cycle cost. Moreover, the self-lubricated dynamic hinge bearings can significantly reduce maintenance costs and provide a low maintenance rotor. 
     However, self-lubricated dynamic hinge bearings are not compatible with existing rotorcraft technology, which utilizes a solid steel hinge sleeve attached to the rotor hinge. Moreover, extensive stress testing and analysis has demonstrated that when the solid steel hinge sleeve is attached to the self-lubricating bearing dynamic hinge, the self-lubricated bearing does not typically align. As a result of this bearing misalignment, the contact stresses on the hinge bearings can peak to unacceptably high levels. This excessive load peaking can significantly reduce the life span of the self-lubricated bearing. Therefore it is necessary to reduce or eliminate load peaking if these types of bearings are to be utilized. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved hinge sleeve member. 
     It is also an object of the present invention to provide a hinge sleeve that reduces the unacceptable levels of load peaking on associated bearings. 
     It is another object of the present invention to provide a low maintenance rotor using self-lubricated dynamic hinge bearings thereby reducing the overall costs and maintenance of the rotor. 
     In accordance with the above and other objects of the present invention, a hinge sleeve for use within a rotor is disclosed. The hinge sleeve includes three cylindrical races functioning as a single unit. The inner race is surrounded by the outer race, and both the inner race and the outer race are formed of a non-elastomeric material. The middle race is positioned between the inner race and outer race and binds the races together. The middle race is elastomeric and allows the inner race and the outer race to rotate relative to each other and accommodates for misalignments during use. This mechanism attenuates the load peaking which is transmitted to the bearing material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the invention will be apparent from the following description and appended claims, reference being made to the accompanying drawings forming a part of the specification, wherein like reference characters designate corresponding parts in the several views: 
     FIG. 1 is a perspective view of a rotor assembly in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is a schematic illustration of the pitch hinge assembly in accordance with a preferred embodiment of the present invention. 
     FIG. 3 is a cross-sectional view of the pitch hinge assembly in FIG.  2 . 
     FIG. 3A is a close up view of the present invention as applied to the pitch hinge assembly in FIG.  2 . 
     FIG. 4 is a perspective view of a pair of bearings attached to a pitch shaft in accordance with a preferred embodiment of the present invention. 
     FIG. 5 is an enlarged cut away view of the pitch hinge components of FIG.  2 . 
     FIG. 6 is a perspective view of a dynamic hinge sleeve in accordance with a preferred embodiment of the present invention. 
     FIG. 6A is a cross-sectional view of a preferred embodiment of the present invention. 
     FIG. 7 is a close-up view of an alternative embodiment of the present invention as applied to the pitch hinge assembly of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention relates to a self-aligning dynamic hinge sleeve member for use with rotorcraft technology. The dynamic hinge sleeve member is preferably utilized in connection with helicopter rotors, but it will be understood that it can have a variety of other uses and applications. Therefore, the present invention is not limited to use only in rotorcraft or helicopters. 
     Turning first to FIG. 1, there is shown a rotor assembly  10  to which the present invention may be applied. As illustrated in FIG. 1, a typical rotor, such as a helicopter blade rotor, comprises an assembly constructed of a main hub member  12  and a plurality of rotor members  14 ,  16 , and  18 . Several hinge assemblies connect the rotor members  14 ,  16 , and  18  in a conventional manner to the main hub member  12 . As FIG. 1 depicts, the hinge assemblies include a horizontal hinge  22 , a vertical hinge  24 , and a pitch hinge  26 . In this embodiment of a rotor assembly, the present invention is directed to the pitch hinge  26 . 
     As shown, in FIGS. 2,  3 , and  3 A, the pitch hinge  26  includes a pitch housing member  32  which encases a pitch shaft member  34 . Attached to the pitch shaft member  34  is at least one pitch hinge bearing  40 . As further illustrated in FIG. 3, a cross-sectional view, the pitch hinge  26  is an assembly that includes the pitch housing member  32 , the pitch hinge bearing  40  and the pitch shaft member  34 , all of which are contiguous with respect to each other. More than one pitch hinge bearing  40 ,  41  may be attached to the pitch shaft member  34 . The pitch hinge  26  transmits forces and moments from the pitch housing member  32  to the pitch shaft member  34  while allowing the pitch housing member  32  to rotate with respect to the pitch shaft member  34 . This results in highly concentrated contact stresses being placed upon the pitch hinge bearing  40 ,  41 . 
     As further shown, in FIG. 3, more than one self-aligning dynamic hinge sleeve member  50 ,  51 , may be attached to the pitch hinge  26  within the rotor. In this position, the self-aligning dynamic hinge sleeve member  50 ,  51  is in contact with the pitch hinge bearing  40 ,  41  which allows the pitch housing member  32  to self-align with the pitch hinge bearing  40 ,  41 . This provides a self-aligning pitch bearing rotor assembly and, as a result, the load peaking (contact stress concentrations) upon the pitch hinge bearing  40 ,  41  can be reduced to an acceptable level. 
     In an alternative embodiment, as shown in FIG. 7, the relative location of the pitch hinge bearing  40 , and the self-aligning dynamic hinge sleeve member  50  can be reversed. Whereas FIGS. 3 and 3A illustrate the self-aligning dynamic hinge sleeve member  50  positioned between the pitch housing member  32  and the pitch hinge bearing  40 , FIG. 7 depicts the self-aligning dynamic hinge sleeve member  50 ′ positioned between the pitch shaft member  34  and the pitch hinge bearing  40 ′. In this embodiment, the pitch housing member  32 , the pitch hinge bearing  40 ′, self-aligning dynamic hinge sleeve member  50 ′, and pitch shaft member  34  are contiguous with respect to each other. 
     In accordance with the present invention, and illustrated further in FIG. 3A, the self-aligning dynamic hinge sleeve member  50 , is comprised of an inner race member  52 , an outer race member  54  surrounding the inner race member  52 , and a middle race member  56 . The middle race member  56  is comprised of an elastomeric or other soft material that allows relative movement between the inner race member  52  and the outer race member  54 . The inner race member  52  has an interior surface  52   a  and an exterior surface  52   b . The outer race member  54  also has an interior surface  54   a  and an exterior surface  54   b . A flange  58  on the exterior surface  54   b  of the outer race member  54  secures the outer race member  54  to the pitch housing member  32 . The inner race member  52  is in contact with the pitch hinge bearing  40 . 
     Although FIG. 3A shows the self-aligning dynamic hinge sleeve member  50  being attached to the pitch housing member  32  and the self-aligning dynamic hinge sleeve member  50  being attached by a flange  58 , other attachment locations and configurations may be utilized in accordance with the present invention. 
     As FIG. 4 illustrates, more than one pitch hinge bearing  40 ,  41  may be attached to the pitch shaft member  34 . The pitch hinge bearings  40 ,  41  are attached to the pitch shaft member  34  such as by bolts  44 , as shown in FIGS. 3 and 3A. The embodiment that is depicted in FIG. 4 shows the pitch hinge bearing  41  attached to an end portion  46  of the pitch shaft member  34  and the pitch hinge bearing  40  attached to a central portion  48  of the pitch shaft member  34 . The pitch hinge bearings  40 ,  41  do not rotate on the pitch shaft member  34 . In a preferred embodiment, the pitch hinge bearings  40 ,  41  have a self-lubricating material  42  bonded to the bearing surface. Self-aligning dynamic hinge sleeve members  50 ,  51  are positioned in contact with pitch hinge bearings  40  and  41 , respectively. 
     As illustrated in FIG. 5, the pitch hinge bearings  40 ,  41  are attached to the pitch shaft member  34 , and in contact with exterior surfaces  52   b  and  53   b  of the inner race members  52  and  53  respectively, of the present invention. The outer race members  54 ,  55  are affixed to the pitch hinge member  26  at exterior surfaces  54   b  and  55   b  of the outer race members  54  and  55 , respectively. A flange  58  on the exterior surface  54   b , and a flange  59  on the exterior surface of  55   b  may be utilized as attachment devices. Thus, in a preferred embodiment, as viewed in FIG. 5, an assembled pitch hinge  26  functions when the pitch housing member  32  and self-aligning dynamic hinge sleeve members  50 ,  51  rotate on pitch hinge bearings  40 ,  41  which are attached to the pitch shaft member  34 . As forces and moments are transmitted, from the pitch housing member  32  to the pitch shaft member  34 , the pitch housing member  32  and pitch shaft member  34  each deflect. The inner race members  52 ,  53  of the self-alignment sleeve members  50 ,  51  are allowed to align themselves to the pitch hinge bearings  40 ,  41  due to the elastomeric middle race members  56 ,  57 . This alignment of the inner race members  52 ,  53  and the pitch hinge bearings  40 ,  41  reduces the peak level of contact stresses upon the pitch hinge bearings  40 ,  41 , creating a more uniform contact stress distribution. 
     In a preferred construction, as illustrated in FIGS. 6 and 6A, the self-aligning dynamic hinge sleeve member  50  is comprised of an inner race member  52 , a middle race member  56  and an outer race member  54 . The inner race member  52  has an interior surface  52   a  and an exterior surface  52   b . The outer race member  54  also has an interior surface  54   a  and an exterior surface  54   b , and a flange  58 . The flange  58  is a portion of the exterior surface  54   b  of the outer race member  54 . In a preferred embodiment, the flange  58  of the outer race member  54  secures the dynamic hinge sleeve member  50  to the pitch hinge  26 . The inner race member  52  and the outer race member  54  are bonded together at the interior surfaces  52   a ,  54   a  by the middle race member  56 . The middle race member  56  is comprised of an elastomeric material. In accordance with one aspect of the present invention, the inner race member  52  and outer race member  54  are comprised of a non-elastomeric material. In a preferred embodiment, the inner race member  52  and the outer race member  54  are monolithic metallic structures, but other materials, such as fiber laminated composites, may be employed. 
     In a preferred embodiment, the middle race member  56  of the present invention is comprised of an elastomeric material, either natural rubber, synthetic rubber or a combination. It is conceivable that non-elastomeric materials could also be employed, provided that the middle race member  56  is softer and more compliant than the inner race member  52  and outer race member  54 . The precise selection of materials is within the knowledge of those of ordinary skill in the art. 
     When a self-aligning dynamic hinge sleeve member  50  is attached to the pitch hinge  26  of the rotor assembly, self-lubricating pitch hinge bearings may be used in place of oil bearings. Accordingly, by replacing the oil bearings with self-lubricating bearings, the rotor system requires less maintenance and repair, providing a low maintenance rotor and substantially reducing costs. 
     The present invention also provides a method for minimizing the load peaking on a rotor dynamic hinge bearing. The inventive method comprises positioning a pitch hinge bearing  40  on the pitch shaft member  34 , and further positioning a self-aligning dynamic hinge sleeve member  50  on the pitch hinge bearing  40 . The self-aligning dynamic hinge sleeve member  50  is comprised of an inner race member  52  and an outer race member  54 , and placing the inner race member  52  within the outer race member  54 . Once the inner race member  52  and outer race member  54  are in this stated position, the next step is positioning a middle race member  56  comprised of elastomeric material between the inner race member  52  and outer race member  54 . The elastomeric material is adapted to permit the inner race member  52  and outer race member  54  to have limited rotation and cocking with respect to each other. Subsequently, the pitch shaft member  34  is positioned within the pitch housing cavity  33  inside pitch housing member  32 . In this position the elastomeric middle race member  56  of the self-aligning dynamic hinge sleeve  50  permits the pitch housing member  32  and the pitch shaft member  34  to self-align, and in doing so attenuates the stresses on the pitch hinge bearing  40 . 
     Rotor systems that use oil bearings experience an array of costly and time consuming maintenance problems. A plausible solution that would lower costs and reduce maintenance is to replace the oil bearings with self-lubricating bearings. However, under the current rotor technology, the self-lubricating bearings are stripped of the dry protective lubricant material and therefore unable to function effectively. 
     In an embodiment of the present invention, the self-aligning dynamic hinge sleeve utilizes a layer of elastomeric material trapped between two non-elastomeric race members. The selection of both the geometry and stiffness of the elastomeric material allows limited rotation and cocking with respect to each other, and permits the pitch housing member  32  to self-align with the pitch hinge bearings  40 . 
     As a result, the contact stress peaking transmitted from the self-lubricated dynamic pitch hinge to the self-lubricated bearing can be significantly reduced when the self-aligning dynamic hinge sleeve is used in place of the solid steel hinge sleeve. This improvement brings stresses that far exceeded the self-lubricated bearing materials allowable, down to a level that is acceptable. This in turn substantially increases the bearing life. 
     The present invention is a novel method and apparatus that permits self-lubricating bearings to function in a rotor system and thereby provide a highly effective rotor system that requires less maintenance and reduces overall costs. 
     While the invention has been described in terms of preferred embodiments, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.