Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Threaded fastener locked to a discreet structure – Recessed or toothed member receiving movable pawl carried by...
Reexamination Certificate
1999-05-28
2001-05-08
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Threaded fastener locked to a discreet structure
Recessed or toothed member receiving movable pawl carried by...
C411S299000, C411S949000, C411S962000
Reexamination Certificate
active
06227782
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a self-locking fastener assembly adapted to secure a plurality of pieces together, and more particularly to a threaded screw fastener assembly provided with a locking element to prevent the threaded fastener assembly from loosening from a workpiece in which it is installed.
BACKGROUND OF THE INVENTION
A variety of locking threaded fasteners or fastening assemblies are known in the art. The goal of such systems is to prevent the male and female components of the fastening assemblies from loosening and coming apart when subjected to vibration, expansion, contraction and other possible movement. Most such systems rely on provision of increased friction to provide improved thread locking. Such systems include thread coatings such as LOCTITE® thread coatings, and/or other products to create a locking friction between the male and female threads, and/or an increased locking friction between the head of a fastener and the surface of a workpiece to which it is fastened. Some systems employ a mechanical locking system to maintain the respective positions of the male and female fastener components. One example of a known mechanical system is a locking nut, in which is positioned a collar with a plurality of flexible arms extending inwardly; these arms seat in longitudinal channels formed on the outer periphery of the threaded male fastener. Upon engagement of the arms with respective channels, loosening is prevented by preventing relative rotation of the components in a loosening direction. The above described structure is illustrated in U.S. Pat. No. 5,238,342 issued to Stencel.
A typical fastener application in automotive applications using plastic materials involves a metal or plastic screw that is used to secure a component to a plastic workpiece. A problem in such applications is that axial loads resulting from torque are concentrated on a relatively narrow region of the boss surrounding the male screw fastener, causing potential for damage by cracking the workpiece. In many such applications, a metal sleeve or insert is provided in the plastic workpiece to provide for distribution of the force applied in fastening, and to prevent damage by the male fastener to the workpiece. There are significant drawbacks to the use of such inserts. The use of such inserts is expensive, requiring purchase or fabrication of an additional separate component, and the installation thereof in the boss before the screw fastener can be used. This slows the manufacturing speed by requiring the additional manufacturing steps of installing numerous inserts in the plastic workpiece where the fastening will occur. In addition to being expensive, such inserts are prone to pullout from the plastic workpiece at relatively low levels of force. Thus, a component fastened to a plastic workpiece where an insert is used may be less securely installed than would be optimal. For example, in a thermoset plastic, the pullout forces required to remove an insert may actually be less than that needed to remove a screw properly screwed into the workpiece. Finally, the use of inserts impedes recycling of the plastic workpiece in the event the workpiece is disassembled, because the metal sleeve or insert must be drilled out of or punched from the plastic workpiece before the plastic can be recycled.
A common problem encountered in fastener applications used in plastic workpieces arises when the fastener is to operate as a stud onto which another component is to be mounted, and is secured with a nut. One risk is the cross-threading of the nut on the stud, which can result in the nut locking up or seizing on the stud. Continued tightening of a cross-threaded nut can cause turning of the self-tapping threads of the screw, thereby potentially damaging the boss. In the same way, if a nut bottoms out on the stud mounted onto the plastic workpiece, there is the distinct possibility that the nut will strip or otherwise damage the boss.
Therefore, there is a need for a locking screw fastener adapted for use in mounting particularly (though not exclusively) to plastic workpieces; such locking screw fasteners should not require metal inserts or sleeves to be inserted in the workpiece; and they should be adapted to prevent damage to the workpiece in the event of cross-threading or overtorquing of a nut onto a stud portion of the fastener.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a self-locking fastener assembly overcoming drawbacks of the known prior art.
It is another object of the invention to provide a locking element preventing undesirable loosening of the self-locking assembly of the present invention.
It is still another object of the invention to provide a locking element eliminating excessive torque values upon a workpiece to prevent damage to the workpiece.
It is a further object of the invention to provide a self-locking fastener assembly that is removable, and in some instances, reusable, allowing easy servicing or recycling of a workpiece in which it was installed.
It is still a further object of the present invention to provide a self-locking stud assembly which is able to prevent damage to the workpiece, particularly (though not exclusively), a plastic workpiece, in the event of overtorquing of a nut on the stud of the assembly, and which is removable in the case of cross-threading of a nut on the stud assembly.
The invention addresses these and other drawbacks in known prior art fastening assemblies and meets these needs with a novel fastening assembly. Generally, the assembly, according to the invention, comprises a male screw fastener (or a female nut fastener) with a locking element, which has a plurality of flexible fingers extending radially outwardly and angularly from the body of the male screw fastener (or female nut fastener). The male screw fastener (or female nut fastener) mates with a female component. The female component is formed with a cavity whose walls are shaped to form notches for receiving and engaging the fingers. By appropriate selection of the number, size, and composition of the fingers, and the shapes of the cavity walls that engage with them, the amount of torque required to loosen a secured fastener can be selected for a particular application as desired.
Referring to the embodiment using a male screw fastener, the male fastener can comprise, but is not limited to, a stud, bolt or screw, whereas the female component can be incorporated within a nut, casting, stamping, molded part and the like and includes a variety of apertures. In a preferred embodiment, where the female component is a plastic workpiece with an aperture therein, the area of the plastic workpiece surrounding the aperture is referred to as the boss. The aperture has an inner diameter sufficient to receive the shank of the male screw fastener, and is provided in an upper portion with the above described cavity whose walls engage with the fingers of the locking element of the male screw fastener. A plate is preferably provided around the shank of the male screw fastener to disseminate torque loads typically concentrated on the boss. Such load dispersion allows higher torque values to be applied without damaging the boss.
The locking element of the male screw fastener can be integrally formed with, or separately manufactured and mounted to, any region along the entire length of the male screw fastener including a head and shank thereof. Many variations of attachment of the locking element to the male screw fastener may include, for example, press-fitting, swaging, slotting, riveting, welding, gluing, or molding.
The locking element used in the invention is effective in a variety of materials, and the male and/or female components can be made of plastic, composite, metal or any other material suitable to meet the needs for the fastening assembly. Where the male screw fastener is made of a plastic or composite material, it is feasible to mold the male screw fastener including the locking element as a unitary product.
In a preferred embodiment, the m
Bowling Stephen
Feick W. Kurt
St. Onge Steward Johnston & Reens LLC
Wilson Neill
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