Abstract:
A composite drive shaft in which the end adapters are captured in the composite material portion during the process of manufacturing of the composite drive shaft assembly is disclosed. The end adapters include lugs that protrude outward longitudinally to transmit torque, tensile, and compressive forces, and bending moments to the composite material portion and vice versa. To increase the load carrying capacity for axial force and bending moment, the end adapters may have at least one recessed circumferential groove. Before the manufacturing process, one or more bonding agents may be applied onto the interface of the end adapter to enhance the performance of engagement between the end adapters and the composite material portion. The composite material portion and end adapters are co-cured to produce a final drive shaft that requires no additional work for assembly.

Description:
TECHNICAL FIELD 
   The present invention relates to composite drive shafts. 
   DESCRIPTION OF THE PRIOR ART 
   Composite drive shafts have been in use for many years. Because they are lighter than metallic drive shafts, they are particularly useful in industries where weight is a significant concern, such as in the aircraft industry and the automotive industry. Composite drive shafts usually consist of a composite material portion with a metallic end adapter connected to each end of the portion. 
   One the of the biggest challenges associated with composite drive shafts is connecting end adapters to the composite material portion. There are basically three ways to connect the end adapters to the composite material portion: (1) by mechanically bolting the end adapters to the composite material portion; (2) by clamping or biting into the composite material with a serrated end adapter; and (3) by adhering the end adapter to the composite material portion. The first method is currently used in the aircraft industry, the second method is currently used in the automotive industry, and the third method can only be used in low torque applications. 
   All of these methods have significant disadvantages. Mechanically bolting the end adapters to the composite material portion is very labor intensive and expensive. The mechanical bolts increase the part count associated with the shaft, and add weight to the shaft. In addition, bolt holes must be drilled through the composite material and end adapter, which can lead to crack initiation and propagation causing potential failure of the shaft. Clamping or biting into the composite material portion with a serrated end adapter diminishes the integrity of the composite material and reduces the strength of the drive shaft. As for adhering the end adapters to the composite material portion by adhesive, this method is limited to low torque applications. Moreover, the adhesive joint may not function properly when undetectable a manufacturing defect exists, or when improper handling occurs during service. 
   Thus, although the foregoing represent great strides in composite drive shaft technology, many shortcomings remain. 
   SUMMARY OF THE INVENTION 
   There is a need for a composite drive shaft with captured end adapters. 
   Therefore, it is an object of the present invention to provide a composite drive shaft in which the end adapters are captured in the composite material portion during the process of manufacturing. 
   This object is achieved by providing a composite drive shaft in which the end adapters are captured in the composite material portion during the process of manufacturing. 
   The composite drive shaft according to the present invention provides significant benefits and advantages, including: (1) the costs of manufacturing the shaft are lower; (2) the shaft is less susceptible to corrosion; (3) the shaft has greater strength; (4) the shaft is lighter; (5) because the end adapters do not clamp or bite into the composite material, the integrity of the composite material is maintained; (6) because bolts are not necessary, fewer parts are necessary; (7) because bolt holes are not drilled through the composite material and end adapters, crack initiation and propagation is greatly reduced; (8) the shaft can be used in high speed and high torque applications; (9) post-cure cutting and machining of the composite material portion are minimized; and (10) the end adapters can be recovered from defective or damaged assemblies and re-used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention 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 perspective view of a helicopter having a composite drive shaft with captured end adapters according to the present invention; 
       FIG. 2A  is a plan view of a tilt rotor aircraft having a composite drive shaft with captured end adapters according to the present invention in an airplane mode; 
       FIG. 2B  is a perspective view of another tilt rotor aircraft having a composite drive shaft with captured end adapters according to the present invention in a helicopter mode; 
       FIG. 3  is a perspective view of a quad tilt rotor aircraft having a composite drive shaft with captured end adapters according to the present invention in the airplane mode; 
       FIG. 4  is an isometric view of the composite drive shaft with captured end adapters according to the present invention; 
       FIG. 5  is an isometric view of one of the end adapters of the composite drive shaft of  FIG. 4 ; 
       FIG. 6  is a side view of the end adapter of  FIG. 5 ; 
       FIG. 7  is a cross-sectional view of the end adapter of  FIG. 6  taken at VII-VII. 
       FIG. 8  is a cross-sectional view of the adapter-tube interface of the composite drive shaft taken at VIII-VIII of  FIG. 4 . 
       FIG. 9  is a partial longitudinal cross-sectional view of the composite drive shaft of  FIG. 4 . 
       FIG. 10  is a perspective view of an alternate embodiment of the end cap of  FIG. 5 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1  in the drawings, a helicopter  11  having a composite drive shaft with captured end adapters according to the present invention is illustrated. Helicopter  11  has a fuselage  13  and a main rotor assembly  15 , including main rotor blades  17  and a main rotor shaft  18 . Helicopter  11  has a tail rotor assembly  19 , including tail rotor blades  21  and a tail rotor shaft  20 . Main rotor blades  17  generally rotate about a longitudinal axis  16  of main rotor shaft  18 . Tail rotor blades  21  generally rotate about a longitudinal axis  22  of tail rotor shaft  20 . Main rotor blades  17  and tail rotor blades  21  are driven by a drive means  25  carried by fuselage  13 . Torque is transmitted from drive means  25  to tail rotor assembly  19  through at least one composite drive shaft having captured end adapters that is disposed within a tail boom  27 . 
   The present invention may also be utilized on other types of rotary wing aircraft. Referring now to  FIGS. 2A and 2B  in the drawings, a tilt rotor aircraft  111  according to the present invention is illustrated. As is conventional with tilt rotor aircraft, rotor assemblies  113   a  and  113   b  are carried by wings  115   a  and  115   b , and are disposed at end portions  116   a  and  116   b  of wings  115   a  and  115   b , respectively. Tilt rotor assemblies  113   a  and  113   b  include nacelles  120   a  and  120   b , which carry the engines and transmissions of tilt rotor aircraft  111 , as well as, rotor hubs  119   a  and  119   b  on forward ends  121   a  and  121   b  of tilt rotor assemblies  113   a  and  113   b , respectively. 
   Tilt rotor assemblies  113   a  and  113   b  move or rotate relative to wing members  115   a  and  115   b  between a helicopter mode in which tilt rotor assemblies  113   a  and  113   b  are tilted upward, such that tilt rotor aircraft  111  flies like a conventional helicopter; and an airplane mode in which tilt rotor assemblies  113   a  and  113   b  are tilted forward, such that tilt rotor aircraft  111  flies like a conventional propeller driven aircraft. In  FIG. 2A , tilt rotor aircraft  111  is depicted as a civilian-type tilt rotor aircraft, and is shown in the airplane mode; and in  FIG. 2B , tilt rotor aircraft  111  is depicted as a military-type tilt rotor aircraft, and is shown in the helicopter mode. As shown in  FIGS. 2A and 2B , wings  115   a  and  115   b  are coupled to a fuselage  114 . Tilt rotor aircraft  111  includes at least one composite drive shaft having captured end adapters that passes through wings  115   a  and  115   b  and fuselage  114  from tilt rotor assembly  113   a  to tilt rotor assembly  113   b.    
   Referring now to  FIG. 3  in the drawings, a quad tilt rotor aircraft  211  having a composite drive shaft with captured end adapters according to the present Invention is illustrated. As with the tilt rotor aircraft of  FIGS. 2A and 2B , tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d  are carried by wings  215   a ,  215   b ,  215   c , and  215   d , respectively. Tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d  include nacelles  220   a ,  220   b ,  220   c , and  220   d , which carry the engines and transmissions of quad tilt rotor aircraft  211 , as well as, rotor hubs  219   a ,  219   b ,  219   c , and  219   d  on forward ends of tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d , respectively. 
   Tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d  move or rotate relative to wing members  215   a ,  215   b ,  215   c , and  215   d  between a helicopter mode in which tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d  are tilted upward, such that quad tilt rotor aircraft  211  flies like a conventional helicopter; and an airplane mode in which tilt rotor assemblies  213   a ,  213   b ,  213   c , and  213   d  are tilted forward, such that quad tilt rotor aircraft  211  flies like a conventional propeller driven aircraft. In  FIG. 3 , quad tilt rotor aircraft  111  is shown in the airplane mode. As shown in  FIG. 3 , wings  215   a ,  215   b ,  215   c , and  215   d  are coupled to a fuselage  214 . Quad tilt rotor aircraft  211  includes at least one composite drive shaft having captured end adapters that passes through wings  215   a  and  215   c  and fuselage  214  from tilt rotor assembly  213   a  to tilt rotor assembly  213   c , and/or at least one composite drive shaft having captured end adapters that passes through wings  215   b  and  215   d  and fuselage  214  from tilt rotor assembly  213   b  to tilt rotor assembly  213   d . Quad tilt rotor aircraft  211  may also include at least one composite drive shaft having captured end adapters that passes through fuselage  214  in the fore and aft direction connecting the shaft system in forward wings  215   a  and  215   c  to the shaft system in aft wings  215   b  and  215   d.    
   It should be understood that the present invention may be used with any aircraft on which it would be desirable to have a composite drive shaft with captured end adapters according to the present invention, including unmanned aerial vehicles that are remotely piloted. In addition, it will be appreciated that the present invention may be used in non-torque applications, such as an aircraft refueling boom or a landing gear actuator shaft. The composite drive shaft with captured end adapters may also be in other industries beside the aircraft industry, such as the automotive industry and the manufacturing industry. Indeed, the present invention may be used in any application in which it is desirable to have a low-weight, high-strength, high-speed, and/or high-torque composite drive shaft. 
   Referring now to  FIGS. 4 and 9  in the drawings, a drive shaft assembly  311  comprising a composite material portion, referred to herein as a composite tube  313 , and captured end adapters  315   a  and  315   b  according to the present invention is illustrated. End adapters  315   a  and  315   b  are captured in composite tube  313  at end portions  317   a  and  317   b  of composite tube  313 , respectively, during the process of manufacturing composite tube  313 . In the preferred embodiment, composite tube  313  is a braided fiber and resin transfer molded component. Such components are typically more damage tolerant and have a higher ballistic survivability. The braided fiber may be either a two-dimensional or a three dimensional braided fiber. However, it should be understood that composite tube  313  may also be manufactured by filament winding, fiber placement, or any other processes that are deemed appropriate. 
   Although end adapters  315   a  and  315   b  are shown as being identical in shape and form, it will be appreciated that composite tube  313  may be manufactured such that end adapters  315   a  and  315   b  may be of different types, shapes and sizes to facilitate connection to a wide variety of different driving and driven components. 
   Referring now to  FIGS. 5-7  in the drawings, end adapter  315   a  is illustrated prior to being captured during the process of manufacturing composite tube  313 . It should be understood that any discussion or description herein of end adapter  315   a  applies equally to end adapter  315   b , and vice versa. End adapter  315   a  is preferably formed from a metallic material, such as aluminum, titanium, or steel, but may be formed from any other suitable rigid material, including non-metallic material. 
   End adapter  315   a  preferably includes an interface portion  319  that is configured to be coupled to the end adapter of a driving or driven shaft or component (not shown). As is shown, interface portion  319  includes a plurality of optional spaced apart engagement teeth  321  and fastener holes  323 . It will be appreciated that optional engagement teeth  321  and fastener holes  323  are representative of any type of clamping or clasping means for coupling end adapter  315   a  to the driving or driven shaft or component. Interface portion  319  transitions into a neck portion  325 . Neck portion  325  may be configured in a wide variety of cross-sectional shapes and sizes, depending upon the desired application. For example, as is shown, neck portion  325  has a reduced cross-sectional area. This allows clearance for and easy access to fasteners (not shown) that pass through fastener holes  323 . It will be appreciated that in some applications, neck portion  325  may not be necessary. End adapter  315   a  terminates opposite interface portion  319  with an interior end  326 . 
   End adapter  315   a  includes an adapter-tube interface  327  that is configured to engage composite tube  313 . In the preferred embodiment, adapter-tube interface  327  comprises a plurality of lugs  329  spaced around the periphery of adapter-tube interface  327 . Lugs  329  protrude radially outward to engage the interior surface of composite tube  313 , as is shown in  FIG. 8 , between lugs  329  and composite laminate  351 . Each lug  329  includes a lug face  331 , opposing lug flanks  333 , and opposing lug ends  335 . Lugs  329  are separated by a generally longitudinal groove having a bottom that is referred to herein as a lug base  337 . 
   Lug faces  331  form circumferentially exterior top surfaces that engage the circumferentially interior surface of composite tube  313 , as shown in  FIG. 8 . Lug faces  331  may be smooth, flat, or curved. Opposing lug flanks  333  are preferably radially aligned longitudinal surfaces having filet radii. As will be explained in more detail below, the filet radii function to reduce stress concentration and provide a smooth transition for the fibers of composite tube  313 . Opposing lug flanks  333  function to transmit torque from end adapter  315   a  to composite tube  313  and vice versa. The leading lug flank  333  of one lug  329  and the trailing lug flank  333  of the adjacent lug  329  form an angle A. The number of lugs  329  and angle A are determined by the design requirements of the drive shaft, including the load and stress distributions for optimized drive shaft strength, and the method of mating the drive shaft with other components or shafts. It will be appreciated that lug flanks  333  may be angled with respect to an axis  334  of the drive shaft, or may be crowned. In this manner, lead correction can be applied to lugs  329 . Opposing lug ends  335  transition from neck portion  325  at one end and from interior end  326  at the opposing end, and taper toward each other with increasing radial distance. Opposing lug ends  335  function to support axial tensile and compressive loads and bending moments. It will be appreciated the taper of lug ends  335  may be steep, such as 90°, to carry additional axial forces and bending moments. Lug bases  337  may be flat, smooth, or curved. 
   Although end adapter  315   a  is shown disposed partly within composite tube  313  and partly outside of composite tube  313 , it should be understood that end adapter  315   a  may be disposed entirely within composite tube  313 , and may include an internal interface portion. 
   In an alternate embodiment, lugs  329  are hollowed out, as is indicated by the dashed line  339  in  FIG. 7 . This hollowing out of one or more of lugs  329  reduces the weight of end adapter  315   a.    
   As shown in  FIG. 10 , in another alternate embodiment, at least one circumferential groove  330  across lug faces  331  (not shown) and extending radially inward from lug faces  331  may be included to further facilitate bending moments. In such embodiments, it is preferred that the circumferential grooves extend radially inward to lug base  337 . 
   Referring now to  FIG. 8  in the drawings, end adapter  315   b  interfaced with composite tube  313  is shown in a cross-sectional view taken at VIII-VIII of  FIG. 4 . As is shown, lugs  329  of end adapter  315   b  are captured by the layers of composite laminate  351  that is part of composite tube  313 . As set forth above, in the preferred embodiment, composite laminate  351  is a braided composite. This capturing process is performed during the process of laying up and manufacturing composite tube  313 . In the preferred embodiment, lugs  329  are entirely surrounded by braided fibers  351 . The layering of composite laminate  351  down to lug bases  337  between lug flanks  333  provides a positive engagement between composite tube  313  and end adapters  315   a  and  315   b  for the transmission of torque. This configuration eliminates the need to rely solely upon the stiffness of the components and/or the adhesion between the components to transfer the torque, as is required in hexagonal connections and circular connections with adhesive. Filets  353  at the intersection of lug flanks  333  and lug bases  337  aid in reducing stress concentrations in composite laminate  351  and lugs  329 . Filets  353  also provide a smooth transition from lug bases  337  to lug flanks  333  to prevent a resin rich situation at the intersection. 
   The preferred process of manufacturing drive shaft assembly  311  will now be described. First, end adapters  315   a  and  315   b  of a selected configuration are placed on an elongated mandrel. Then, composite tube  313 , which comprises polymer or plastic fibers, is applied over the mandrel and end adapters  315   a  and  315   b  by an appropriate braiding technique, such as two-dimensional or three dimensional braiding, to form a composite preform. In some applications, it may be desirable to place an adhesive film on the adapter-tube interface between end adapter  315   a  and the polymer or plastic fibers, so that the adhesive is disposed between end adapter  315   b  and composite tube  313 . Next, one or more tools or molds configured to match the composite preform, including end adapters  315   a  and  315   b , the mandrel, and the composite tube  313 , are clamped down over the entire assembly. Then, the assembly is heated, evacuated, injected with resin, and cured to form drive shaft assembly  311 . 
   As set forth above, in alternate embodiments, composite tube  313  may be formed by other means, such as filament winding, filament placement, or any other type of composite manufacturing technique. In such instances, pre-impregnated fibers are applied over the mandrel and end adapter  315   b  by filament winding or filament placement processes. The assembly is then enclosed in vacuum bags and evacuated. Next, the resin is cured. Then, the vacuum bags and mandrel are removed. 
   Because no fasteners are required, no drilling of fastener holes is necessary, and no fasteners protrude outward. This reduces the possibility of interference with electrical lines, hydraulic lines, and other components when installed and operated on the aircraft. The only post-cure processing that is required is simple trimming of the exposed ends of composite laminate  351 . By manufacturing drive shaft assembly  311  in this manner, misalignment of end adapters  315   a  and  315   b  is greatly reduced, and little or no balance correction is required. 
   It will be appreciated that end adapters  315   a  and  315   b  can be recovered from drive shaft assembly  311  by simply burning off composite laminate  351 , should any drive shaft assembly  311  either contain a manufacturing defect, or become damaged during use. This ability to recover and re-use end adapters  315   a  and  315   b  represents tremendous savings in labor, time, and cost. 
   The composite drive shaft according to the present invention provides significant benefits and advantages, including: (1) the costs of manufacturing the shaft are lower; (2) the shaft is less susceptible to corrosion; (3) the shaft has greater strength; (4) the shaft is lighter; (5) because the end adapters do not clamp or bite into the composite material, the integrity of the composite material is maintained; (6) because bolts are not necessary, fewer parts are necessary; (7) because bolt holes are not drilled through the composite and end adapters, crack initiation and propagation is greatly reduced; (8) the shaft can be used in high speed and high torque applications; (9) post-cure cutting and machining of the composite tube are minimized; and (10) the end adapters can be recovered from damaged assemblies and re-used. 
   It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention 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.