Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Headed fastener element with nut – washer – securing means or cap – Metallic resilient securing means
Reexamination Certificate
2001-02-02
2003-07-01
Wilson, Neill (Department: 3679)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Headed fastener element with nut, washer, securing means or cap
Metallic resilient securing means
C411S361000, C411S533000, C411S999000, C029S437000, C029S510000
Reexamination Certificate
active
06585468
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to threaded fastener assemblies and, more particularly, to assemblies in which the fastener is captivated within the workpiece.
BACKGROUND OF THE INVENTION
A common goal among manufacturers is to increase productivity by reducing the production time of an assembly process. In an effort to achieve this goal, captivated fastener assemblies are often employed. Such captivated fastener assemblies utilize fasteners which can be pre-attached to a workpiece that later is fastened to a support structure during the assembly process. Because attempts to find lost or misplaced screws are both inconvenient and time consuming, captivated fastener assemblies are used to help reduce the production time of an assembly process and wasted worker effort that is caused by searching for these lost or misplaced screws. In addition, captivated fastener assemblies can ease workpiece installation processes by holding the fastener within the workpiece in proper position to allow a worker to expediently secure the workpiece to the support structure.
Many captivated fastener assemblies have previously been designed in which the fastener is retained within the washer to prevent separation.
FIGS. 1 and 2
illustrate a known captivated fastener assembly which is used to secure a valve cover (not shown) to an engine cylinder head (not shown). The assembly
10
generally includes three pieces: fastener
12
, sleeve
14
and grommet
16
. It is necessary that the fastener
12
be able to slide axially within the bore of the sleeve
14
. On the other hand, it is also important that the assembly
10
remain assembled and not fall apart during shipment or when the cover is mounted to the engine cylinder head. Thus, there is a requirement that the fastener
12
be captivated within the workpiece. A common commercially used design for accomplishing these goals employs a protuberance, such as enlarged ring
18
, formed on the fastener shank which cooperates with a reduced diameter section
20
formed in the sleeve
14
. The outer diameter of the ring
18
and inner diameter defined by the sleeve section
20
are such that the fastener can be pushed through the sleeve so that the ring
18
falls below section
20
yet there still remains a sufficient interference between the ring
18
and section
20
to prevent the ring (and thus the fastener) from again passing upwardly past section
20
which otherwise would permit separation of the fastener
12
from the sleeve
14
.
The captivated fastener assembly disclosed in U.S. Pat. No. 4,732,519 employs a similar type of the above-mentioned arrangement. The captivated fastener assembly disclosed in this patent includes a fastener, washer, and grommet. A protuberance in the form of a set of wings projects from the shank of the fastener and cooperates with a washer sleeve. The washer sleeve includes an inwardly projecting annular bead portion pre-formed at the top of the sleeve. The wings of the fastener shank are designed to provide an outer diameter that is larger than the inner diameter of the annular bead portion of the sleeve. The fastener is captivated within the washer by forcing the wings of the fastener past the annular bead portion to provide an interference fit, thereby preventing the upward removal of the fastener.
In general, the afore-mentioned captivated fastener assemblies require special steps for forming both the fastener and the washer. For example, the fastener is typically formed by a special thread rolling process. A forging process is normally needed to form the protuberance.
It is very important that tight tolerances be kept during the forming processes. If the difference between the relative diameters is too large, then it could be very difficult or impossible to insert the fastener into the washer sleeve. In contrast, if the diameter of the protuberance of the fastener is too small, then the assembly could become inadvertently separated.
Furthermore, since the captivation process in these types of prior art examples requires that the fastener be forcibly inserted into an aperture, the fastener may axially elongate the grains of the material at the sleeve aperture surface. This action generates an undesirable axially oriented tensile stress gradient in the surface grains. These tensile stress gradients tend to decrease the ductility and fatigue life of the material at the sleeve aperture surface. This method may also cause deformation of portions of the fastener, such as the threads, thereby limiting its fastening effectiveness.
Therefore, it would be desirable to provide a captivated fastener assembly that overcomes one or more of these problems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an assembly in which the fastener is captivated within the workpiece without the need for a distinct outward protuberance on the fastener shank. Thus, a conventional threaded fastener can be used with a workpiece having a deformable sleeve, yet the same goal obtained. The captivation of the fastener is obtained by employing the deformable workpiece sleeve which, before deformation, accepts the shank of the fastener and slides freely along the shank. After the workpiece is slid over the fastener, a plurality of deformed segments are created by applying an inward compressive force to the outside of portions of the sleeve. The inner diameter provided by the deformed segments remains greater than the diameter of the unthreaded portion of the fastener such that a free-flowing fit between the deformed segments and the unthreaded portion of the fastener is provided. Therefore, the fastener is able to move axially relative to the workpiece. However, the inner diameter provided by the deformed segments is less than the outer diameter of the threaded portion of the fastener. Thus, the outer tips of the threads engage the deformed segments if the fastener moves too far upwardly, thereby preventing the fastener from being removed from the workpiece.
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Draper Michael J.
Johnson H. Thad
Harness & Dickey & Pierce P.L.C.
Johnson H. Thad
Wilson Neill
LandOfFree
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