Abstract:
A tamper resistant nut includes a threaded base for engaging a male threaded fastener and a wrenchable body separable from the base. The base has no readily engagable surfaces accommodating standard tools.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present regular United States Patent Application claims the benefits of United States Provisional Application Ser. No. 60/729,146, filed Oct. 21, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to fasteners such as nuts, and, more particularly, the invention pertains to tamper proof nuts.  
       BACKGROUND OF THE INVENTION  
       [0003]     Simple threaded fastening systems, such as a nut and bolt or nut and threaded stud, are used often for ease of installation and low cost. Nut and bolt fasteners can be provided in various shapes and sizes suitable for a particular installation. Nuts and bolts also can be provided in various materials best suited for a particular application.  
         [0004]     Simple threaded fasteners are easy to use and can be provided relatively inexpensively. In some installations, a simple threaded fastener has disadvantages. The fastener may perform acceptably for the securing function it is used for; however, the fastener may not provide the desired level of security. For example, it is desirable in some instances to limit the ability of others to disconnect a fastener so that the items secured thereby cannot be removed or altered. In other installations it is desirable to make it difficult for unauthorized individuals to have access. For example, it is desirable to limit access of vehicle air bag systems to only trained and authorized technicians. Various specialized fasteners requiring specialized, uncommon tools for manipulation have been used in these situations.  
         [0005]     Tamper proof nuts are known; however, some are difficult to install and are costly. A known principle in the design of tamper proof nuts is to provide the nut in shapes that are not easily gripped by hand and not readily engaged by common tools such as wrenches, sockets, pliers and the like. As a result, even for initial installation it may be necessary to have a specialized tool to tighten the nut. Further, manipulating the nut for tightening may be difficult and slow. If the shapes are unusual or non-standard, complex machining may be required to form the nut. Nuts formed by unusual or uncommon techniques can be expensive. If a device or installation requires a large number of fasteners, the use of tamper proof fasteners can increase significantly the cost of the assembly or installation. The difficulty of installation and/or manipulation of a tamper proof fastener can increase labor costs and add further expense to the overall assembly or installation cost.  
         [0006]     It is desirable to provide a fastener that is tamper proof after installation, yet is easy to install quickly with conventional tools. Further, it is desirable that the nut be manufacturable by common fastener manufacturing techniques, and that it be provided inexpensively.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a threaded fastener similar to a nut, but having a dome-shaped flange or main body with a threaded central opening for engaging a threaded bolt or stud. The flange or main body has no readily wrenchable surfaces. A wrenchable body is connected to the flange by a fracture zone configured for separation of the body from the flange when installation is complete.  
         [0008]     In one aspect thereof, the present invention provides a fastener with a base having an exposed surface, a compression surface and a central opening therethrough. A thread is provided in the central opening for engaging a male threaded fastener. A wrenchable body is provided on an opposite side of the base from the compression surface. A failure zone joins the base and the wrenchable body for controlled separation between the base and the wrenchable body.  
         [0009]     In another aspect thereof, the present invention provides a tamper resistant nut with a dome shaped base having a thin outer edge, a thicker central portion and a smooth exposed surface from the central portion to the edge. A central opening extends through the base with a thread in the opening. A body aligned with the central opening projects outwardly of the base exposed surface. The body has peripheral wrench engageable surfaces. A failure zone is defmed in the nut for controlled separation of the body from the base.  
         [0010]     In a still further aspect thereof, the present invention provides a method of making a threaded fastener with steps of forming a dome shaped base having a substantially flat compression surface on one side thereof and a substantially smooth exposed surface on an opposite side thereof, including establishing a thicker central area and a thin outer periphery in the base; forming a central opening through the base from the compression surface to the exposed surface; creating a thread in the central opening; forming a wrenchable body as a part of a monolithic structure including the base; and creating a failure zone in the monolithic structure between the wrenchable body and the base.  
         [0011]     An advantage of the present invention is providing a tamper proof fastener that is easy to install.  
         [0012]     Another advantage of the present invention is providing a tamper proof fastener that can be manufactured inexpensively by common techniques.  
         [0013]     Still another advantage of the present invention is providing a tamper proof nut that can be manufactured by common nut forming techniques, including cold forming and conventional tapping.  
         [0014]     Yet another advantage of the present invention is providing a recessed connection between a frangible drive body and a threaded flange so that the body can be removed without leaving an exposed sharp edge.  
         [0015]     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a perspective view of a tamper proof fastener in accordance with the present invention;  
         [0017]      FIG. 2  is a cross-sectional view of the fastener shown in  FIG. 1 , the cross-sectional view having been taken along line  2 - 2  of  FIG. 1 ; and  
         [0018]      FIG. 3  is a cross-sectional view of the fastener shown in  FIGS. 1 and 2 , illustrating the fastener installed in a fastened system after final tightening has been completed. 
     
    
       [0019]     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use herein of “including”, “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items and equivalents thereof.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring now more specifically to the drawings and to  FIG. 1  in particular a tamper proof nut  10  in accordance with the present invention is shown. As illustrated in  FIG. 1 , tamper proof nut  10  is ready for initial installation.  FIG. 3  illustrates tamper proof nut  10  installed in a fastened system  12  including a bolt  14  and first and second panels  16  and  18 . It should be understood that system  12  shown in  FIG. 3  is merely exemplary in nature, and that tamper proof nuts  10  of the present invention can be used with other types of male threaded fasteners including threaded studs securely mounted in devices, and can be used for securing objects other than panels  16  and  18  as shown. Further, tamper proof nut  10  can be provided in a variety of sizes for use with different size male fasteners and in devices and installations of different types.  
         [0021]     Tamper proof nut  10  is a monolithic body having a base  20  and a wrenchable body  22 . Base  20  defines a central opening  24  having a thread  26  therein for engaging a male fastener component such as bolt  14 . In the exemplary embodiment, base  20  defines a thin, circular outer periphery  28  of insufficient thickness for easy engagement by common tools. Base  20  is thicker near the center thereof and thinner at periphery  28  to establish a smooth, sloping exposed surface  30  for the generally dome-shaped base  20 . A flat, compression surface  32  is provided opposite from wrenchable body  22 . Compression surface  32  confronts the device upon which nut  10  is used and against which nut  10  is tightened during installation. Accordingly, in fastened system  12  shown in  FIG. 3  compression surface  32  is engaged with and confronts panel  18 .  
         [0022]     Wrenchable body  22  defines an axial opening  34  therethrough. Axial opening  34  is of greater diameter than central opening  24  of base  20 . Opening  34  is not threaded and is of sufficient diameter to allow a threaded end of bolt  14  to enter unencumbered and unrestricted. Accordingly, a male fastener component such as bolt  14  does not engage body  22  but can extend upwardly therein when tightening takes place.  
         [0023]     Wrenchable body  22  is configured at the outer surface thereof for engagement by conventional tools. In the exemplary embodiment, wrenchable body  22  is provided with a hex-shaped outer configuration including wrenching surfaces  36 . Accordingly, as seen most clearly in  FIG. 1 , wrenchable body  22  appears similar to a conventional hex nut, except for lacking threads in axial opening  34  thereof. It should be understood that other peripheral shapes and configurations for body  22  also can be used. Further, body  22  can be configured for engagement by other tools including drivers such as screwdrivers and other tools operating at and in the end of body  22  and/or axial opening  34  thereof. To facilitate initial installation, configurations for wrenchable body  22  that are conducive to engagement by common wrenches and hand or power tools are used. However, the present invention also can be used with configurations for less-common types of tools as well.  
         [0024]     Upper surface  34  defines a depression or countersink  40  therein. Wrenchable body  22  is joined to base  20  at a bottom  42  of depression  40 . The area of union between body  22  and base  20  is referred to herein as a failure zone  44  depicted by dashed lines in  FIG. 2 . As part of the process for forming nut  10 , scoring, undercutting or stressing of other types can be provided in failure zone  44  such that a relatively clean break or separation occurs between base  20  and body  22  as described subsequently herein.  
         [0025]     In the use of nut  10 , central opening  24  is aligned with male thread  50  from a male fastener such as bolt  14 , and nut  10  is rotated for engagement of thread  26  and thread  50 . A common wrench, such as a socket wrench, box wrench, end wrench or the like can be used to engage wrenchable body  22  for rotation of nut  10 . Clamping force is applied as compression surface  32  is engaged against panel  18  and nut  10  is tightened. As final tightening force is applied, fracture occurs along failure zone  44 , and wrenchable body  22  separates from base  20 . Through forming techniques, failure zone  44  can be provided so that a specified torque is necessary to cause fracture. As a result, a desired clamp load can be provided in fastened system  12  simply by tightening nut  10  until wrenchable body  22  fractures away from base  20 .  
         [0026]     Even if a portion of bolt  14  extends through base  20  and into body  22 , body  22  can be separated from base  20  in that body  22  has no internal threads and does not physically engage bolt  14 .  
         [0027]     As seen from  FIG. 3 , after wrenchable body  22  has been separated from base  20 , the remaining portion of nut  10  on bolt  14  does not provide readily engagable surfaces or contours for receiving a wrench for turning. Periphery  28  is thin and rounded, thereby making engagement by a wrench difficult. Sloping exposed surface  30  is not conducive to engagement by standard tools.  
         [0028]     By providing failure zone  44  at bottom  42  of depression  40 , the fractured face or edge that remains after body  22  is separated from base  20  is recessed and protected even if a jagged edge remains. Forming body  22  at the bottom of depression  40  concentrates stresses at failure zone  44  for control, consistent separation.  
         [0029]     A tamper proof nut of the present invention can be made of various materials suitable for the application. Because of the simple, yet common shapes of base  20  and body  22 , nut  10  is conducive to standard forming techniques, such as cold forming. Threads  26  can be formed by standard tapping equipment. As a result, nuts  10  of the present invention can be provided at acceptable expense. While easily engaged with standard wrenches during installation, after wrenchable body  22  has been fractured away from base  20  and discarded, the remaining shape is not readily engageable by a wrench. Accordingly, initial installation is facilitated by allowing the use of common tools, yet after installation the fastened connection is secure and not easily tampered with.  
         [0030]     Nut  10  can be formed as a monolithic body of metal including base  20  and wrenchable body  22  integral therewith. Standard forming processes can be used, such as cold forming. Base  20  and body  22  are formed from a single piece of metal with central opening  24  and axial opening  34  formed in substantial alignment one with the other. Central opening  24  is threaded by standard thread forming techniques, such as tapping. Axial opening  34  is formed with a diameter greater than a diameter of central opening  24 . Forming depression  40  in the exposed surface, with wrenchable body  22  formed within depression  40  concentrates stresses along failure zone  44  for controlled separation.  
         [0031]     Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.  
         [0032]     Various features of the invention are set forth in the following claims.