Abstract:
A device for securing a torque bit to a fastener in an object. The novel device includes a structure adapted to apply a force on the torque bit and a mechanism for clamping the structure to the object such that the structure forces the bit to remain engaged with a drive feature of the fastener. In an illustrative embodiment, the structure is bolted to the object, capturing the bit between the structure and the object. Spacers disposed between the structure and the object control the magnitude of the force applied on the bit such that the bit can rotate during torquing. In an alternative embodiment, the structure surrounds the object and is tightened to clamp the structure to the object. An insert disposed between the structure and the bit controls the magnitude of the force applied on the bit in this embodiment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to torque tools. More specifically, the present invention relates to systems and methods for applying torque to structural fasteners. 
         [0003]    2. Description off the Related Art 
         [0004]    Structural fasteners are commonly used to mechanically join two or more objects or parts of an object together. A bolted joint, for example, includes a bolt or cap screw that joins the objects and is secured with a mating thread (on a nut or on one of the objects being joined). The bolt is tightened to a calculated torque, producing a particular preload (the tension in the bolt caused by tightening). Generating sufficient preload is essential for providing a strong and reliable bolted joint that will not loosen or break. The greater the preload (up to the fastener&#39;s maximum preload capability), the greater the strength of the joint. 
         [0005]    It is therefore critical to apply enough torque to set the bolt to the desired preload. Some structural fasteners, however, cannot be pre-loaded to their maximum capability because it is difficult to achieve high levels of torques due to slippage or stripping of the torque interface and torque tools (i.e., torque wrenches and torque bits). 
         [0006]    A higher preload can be achieved by using a larger bolt or a fastener with a drive feature designed for higher torque levels. For example, a hex head drive feature with a protruding hexagonal head can typically sustain more torque than a recessed cross feature (such as a Phillips head). In certain applications, however, it may not be feasible or desirable to use a larger bolt or a bolt with a higher torque drive feature due to various size or design constraints. For example, in the aerospace industry, bolts on an airframe typically need to be flush with the airframe to reduce aerodynamic effects such as drag. Flat-head bolts with a recessed cross drive are therefore typically used in these applications instead of hex head bolts. 
         [0007]    High strength, flat-head bolts are capable of sustaining the high preloads desired in these applications. However, it is difficult to tighten the bolts to the desired preloads using conventional techniques. The resulting preload is usually as low as 50% of the fastener&#39;s capability due to the limited amount of torque that can be applied before the torque tool slips or the drive feature strips. Typically, more “force” by the operator is used to try to keep the torque tool engaged in the fastener drive. But if the tool or drive is worn, it is difficult to achieve even 50% of the desired capability, much less more than that. 
         [0008]    Hence, a need exists in the art for an improved system or method for tightening a fastener that can achieve higher levels of torque than prior approaches. 
       SUMMARY OF THE INVENTION 
       [0009]    The need in the art is addressed by the torque tool aid of the present invention. The novel torque tool aid is a device for securing a torque bit to a fastener in an object. The device includes a structure adapted to apply a force on the torque bit and a mechanism for clamping the structure to the object such that the structure forces the bit to remain engaged with a drive feature of the fastener. In an illustrative embodiment, the structure is bolted to the object, capturing the bit between the structure and the object. Spacers disposed between the structure and the object control the magnitude of the force applied on the bit such that the bit can rotate during torquing. In an alternative embodiment, the structure surrounds the object and is tightened to clamp the structure to the object. An insert disposed between the structure and the bit controls the magnitude of the force applied on the bit in this embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1   a  is a simplified schematic of an illustrative drive feature on a fastener. 
           [0011]      FIG. 1   b  is a simplified schematic of an illustrative torque set bit for applying torque to the fastener of  FIG. 1   a.    
           [0012]      FIG. 2  is a simplified diagram of a torque tool aid device designed in accordance with an illustrative embodiment of the present teachings. 
           [0013]      FIG. 3  is a simplified diagram of a torque tool aid device designed in accordance with an illustrative embodiment of the present teachings. 
           [0014]      FIG. 4  is a three-dimensional view of the illustrative torque tool aid device shown in  FIG. 3 . 
           [0015]      FIG. 5   a  is a simplified diagram of a torque tool aid device designed in accordance with an alternative embodiment of the present teachings. 
           [0016]      FIG. 5   b  is a diagram showing a close up view of part of the torque tool aid device shown in  FIG. 5   a.    
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0017]    Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
         [0018]    While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
         [0019]    The present invention uses a novel device for securing the torque tool in the fastener drive head during torquing. This eliminates the need for the operator to force the torque tool into the drive and allows more effort towards achieving the desired preload. By securing the torque tool into the drive without the additional need of operator force, much higher torques may be achieved without slippage or stripping. 
         [0020]      FIG. 1   a  is a simplified schematic of an illustrative drive feature  12  on a fastener  10 .  FIG. 1   b  is a simplified schematic of an illustrative torque set bit  20  for applying torque to the fastener  10  of  FIG. 1   a . The fastener  10  has a particular drive feature  12  in the head of the fastener  10 . The torque bit  20  has a first end or bit head  22  that is shaped so that it engages the drive feature  12  of the fastener  10 . The other end  24  of the torque bit  20  is attached to a torque wrench or other torque tool (not shown). Turning the torque wrench turns the torque bit  20 , which turns the fastener  10  as long as the bit  20  remains engaged with the drive feature  12 . 
         [0021]    The illustrative drive feature  12  shown in  FIG. 1   a  is a cross-recessed cruciform drive  12  commonly used in the aerospace industry. The present invention may also be applied to other types of drives and fasteners without departing from the scope of the present teachings. 
         [0022]      FIG. 2  is a simplified diagram of a torque tool aid device  30  designed in accordance with an illustrative embodiment of the present teachings. The novel torque tool aid  30  is adapted to retain a torque bit  20  in the drive feature  12  of a fastener  10 , allowing an operator to tighten the fastener  10  by rotating a torque tool coupled to the torque bit  20  without needing to apply additional force to keep the bit  20  engaged with the fastener  10 . This allows the fastener  10  to be tightened to a higher torque—and therefore a higher preload—than can be achieved using conventional techniques. 
         [0023]    In the illustrative embodiment of  FIG. 2 , the fastener  10  joins two parts (for example, a missile airframe  32  and a payload component  34 ) and is secured by a nut plate  36 . In this example, the fastener  10  is a flat-head bolt with a cross-recessed cruciform drive  12 , as shown in  FIG. 1   a . The head of the fastener  10  sits in a countersink  38  in the airframe  32  so that the fastener  10  is flush with or below the surface of the airframe  32 . 
         [0024]    In accordance with the present teachings, the novel torque tool aid  30  includes a bit retaining plate  40  or other structure adapted to hold the torque bit  20  in place, engaged with the drive feature  12  of the fastener  10 . In the illustrative embodiment, the plate  40  has a hole  42  through which the torque bit  20  is inserted so that the bit head  22  is on one side of the plate  40  (toward the fastener  10 ) while the second end  24  of the bit  20  (that couples to the torque wrench) is on the opposite side of the plate  40 . The bit head  22  has a circumference that is larger than the rest of the torque bit  20 , such that when the bit  20  is inserted in the hole  42 , the plate  40  rests against the bit head  22 . 
         [0025]    The torque tool aid  30  is attached to the airframe  32  so that the torque bit  20  is trapped between the plate  40  and the airframe  32 , and the plate  40  applies a predetermined force on the bit  20 , forcing the bit  20  into the drive feature  12  of the fastener  10 . In the embodiment of  FIG. 2 , the torque tool aid  30  is attached to the airframe  32  by two bolts  44  on either side of the torque bit  20 . The bolts  44  may be screwed into holes drilled into the airframe  32  specifically for this purpose, or in the preferred embodiment, the torque tool aid  30  may be designed so that the bolts  44  are screwed into holes  39  already existing in the airframe  32  (for fastening other components, for example). 
         [0026]    The torque tool aid  30  also includes a spacer  46  around each bolt  44 , between the plate  40  and the airframe  32 , for controlling the amount of force the plate  40  applies to the bit  20  so that the bit  20  can rotate. If too much force is applied to the bit  20 , the friction between the plate  40  and the bit head  22  may be too high to torque the bit  20 . If not enough force is applied to the bit  20 , the bit  20  may slip out of the drive feature  12  of the fastener  10 . The thickness of the spacers  46  (i.e., the distance between the plate  40  and the surface of the airframe  32 ) should therefore be sized such that the bit  20  remains engaged in the fastener drive  12 , while also allowing the bit  20  to rotate without too much friction against the plate  40 . 
         [0027]    Optionally, an anti-friction coating  48  may be applied to the plate  40  where the plate  40  is in contact with the bit head  22 , or a bearing  50  (shown in  FIG. 3 ) may be placed between the plate  40  and the bit  20  to reduce friction. 
         [0028]    The bit retaining plate  40  should be made from an appropriate material and sized properly so that the torque bit  20  will remain engaged with the drive feature  12  of the fastener  10  while placing as much torque as is desired onto the fastener  10 . Specifically, the plate  40  should be stiff enough to prevent flexure based on the estimated load associated with the desired torque. Otherwise, if the plate  40  flexes or bends during torquing, the bit  20  may ride out of the drive feature  12 . In an illustrative embodiment, the plate  40  is made from metal or plastic. The spacers  46  may be made from the same material as the plate  40 , or from a different material. 
         [0029]    In the embodiment of  FIG. 2 , the torque tool device  30  is adapted to retain only one torque bit  20 . The device  30  may also be designed to retain several bits  20  simultaneously to simplify installation and use, depending on the application.  FIG. 3  illustrates how the torque tool aid of the present invention might be customized for a particular illustrative application. 
         [0030]      FIG. 3  is a simplified diagram of a torque tool aid device  30  designed in accordance with an illustrative embodiment of the present teachings.  FIG. 4  is a three-dimensional view of the illustrative torque tool aid device  30  shown in  FIG. 3 . In this example, three payload bolts  10  joining an airframe  32  and a payload component  34  need to be tightened to a torque of about 200 in-lbs to prevent joint slippage (numerical examples are given for illustrative purposes only). The payload bolts  10  have a capability of about 260 in-lbs, but can only be tightened to 125 in-lbs using just a torque wrench without the torque tool aid  30 . The airframe  32  also includes three bolt holes  39  near the payload bolts  10 , for attaching other components to the airframe  32 . 
         [0031]    In accordance with the present teachings, a torque tool aid  30  is customized for this example application by designing a bit retaining plate  40  that attaches to the airframe  32  using attach bolts  44  that screw into the bolt holes  39 . The bit retaining plate  40  includes three holes  42  for holding three torque bits  20 . The torque tool aid  30  may also include a bearing  50  placed around each torque bit  20 , between the bit head  22  and the bit retaining plate  40 , for reducing friction. In the embodiment of  FIG. 3 , a clip  52  is placed around each bit  20 , on the side of the plate  40  opposite the bit head  22 , to prevent the bits  20  from falling out of the plate  40 . 
         [0032]    In a preferred embodiment, the attach bolts  44  are socket head cap screws with a drive feature matching that of the payload bolts  10  so that a common torque tool can be used to install the torque tool aid device  30  and to tighten the payload bolts  10 . 
         [0033]    In operation, the payload component  34  is joined to the airframe  32  and the three payload bolts  10  are tightened using a torque wrench (to about 125 in-lbs). The torque tool aid  30  is then attached to the airframe  32  by the attach bolts  44 , with the three torque bits  20  captured between the bit retaining plate  40  and the airframe  32  such that the bits  20  are engaged with the drive features  12  of the fasteners  10 . The torque wrench is then coupled to each torque bit  20 , and the payload bolts  10  are torqued to the desired torque. The torque tool aid  30  and torque bits  20  are then removed, leaving the airframe bolt holes  39  free for their original purpose. 
         [0034]      FIG. 5   a  is a simplified diagram of a torque tool aid device  30 ′ designed in accordance with an alternative embodiment of the present teachings. In this embodiment, the torque tool aid  30 ′ is shaped so that it slides over and around the components being fastened, instead of being bolted to one of the components as in the embodiments of  FIGS. 2-4 . In the example shown in  FIG. 5 , the fasteners  10  are in a round missile airframe  32 ′, and the torque tool aid  30 ′ is a ring that fits around the missile body  32 ′. 
         [0035]      FIG. 5   b  is a diagram showing a close up view of part of the torque tool aid device  30 ′ of  FIG. 5   a . The torque tool aid  30 ′ includes a bit retaining plate  40 ′, which in this embodiment is shaped as a ring that goes around the circumference of the missile airframe  32 ′. The bit retaining ring  40 ′ includes a hole or cutout  42  through which the torque bit  20  is inserted such that the ring  40 ′ holds the bit  20  engaged with the drive feature  12  of the fastener  10 . Instead of being clamped to the airframe  32 ′ by bolts, the ring  40 ′ is tightened around the missile body  32 ′, such that the bit  20  is held in place by the ring  40 ′ using the force from the opposite side of the ring  40 ′. The ring  40 ′ may also include a mechanism (not shown) for tightening and loosening the ring  40 ′. 
         [0036]    An insert  54  is attached to the ring  40 ′ between the bit head  22  and the ring  40 ′. The insert  54  serves a similar purpose as the spacer  46  in the previous embodiments, controlling the amount of force placed on the bit  20  to retain the bit  20  in the fastener drive  12  while allowing the bit  20  to rotate without too much friction. In an illustrative embodiment, the insert  54  is threaded, allowing it to be screwed into the ring  40 ′. The insert  54  may be fabricated from a material or coated with a material designed to reduce friction at the bit-insert interface during torquing. The torque tool aid  30 ′ may also include a bearing placed between the bit  20  and the insert  54  to reduce friction. 
         [0037]    The ring  40 ′ may include holes or cut-outs  42  at multiple locations to simultaneously hold multiple torque bits  20  (to easily tighten multiple fasteners, as in the embodiments of  FIG. 3-4 ), or it may be adapted to hold just one torque bit  20 , in which case after one fastener is torqued, the ring  40 ′ would be loosened, rotated to place the bit  20  on the next fastener, and re-tightened, allowing the next fastener to be torqued. The torque tool aid  30 ′ may also be designed to fit any shape, not just a round ring. 
         [0038]    Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
         [0039]    It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
         [0040]    Accordingly,