1. Field of the Invention
The present invention relates to captive fastener assemblies, and more particularly, to an improved captive fastener assembly suitable for being captivated to panels such as aircraft panels and the like.
2. Description of the Prior Art
Panel fasteners for aircraft cowlings and other aircraft panels are well known in the art. In the customary means of assembly, a stud with an enlarged head is inserted through the opening of the panel and into a nut member attached to the base structure of the aircraft. The stud is then torqued to secure the panel. To prevent the stud from falling out of the panel when removed from the nut and possibly being lost, or falling into a jet engine intake and thereby damaging the engine, the stud is usually coupled with a retaining means which captivates the stud to the panel.
Once such captivated panel fastener is shown in U.S. Pat. No. 3,294,140. As seen in this patent, the stud has an enlarged head and three splines extending intermediate its length. A retaining ring formed with integral tabs is snapped over the unsplined leading end of the stud and the tabs placed in the splines. Once in place, the retaining ring and the enlarged head of the stud function as stops to captivate the stud and prevent it from being displaced from the panel. In this embodiment, the retaining ring must be relatively flexible, and the tolerances between the tabs and the spline must be relatively loose to permit the ring to be snapped over the leading end of the stud.
Because of the flexibility of the retaining ring and the loose tolerances between the splines and the tabs, it has been found that the stud, particularly if cocked at an angle, can become accidentally detached from the retaining ring and thus from the panel. As mentioned above, this has important consequences if the stud were to fall into the jet engine intake and damage the engine.
Other prior art techniques for installing retaining rings with inward facing tabs onto studs (screws) having longitudinal slots to accept the tabs included:
(a) Using a split retaining ring which is open sufficiently to clear a screw nose abutment and then allow to close with the tangs engaging the screw slots. This method of ring installation is prone to assembler error which would cause the ring to take a "set" in the open position resulting in disengagement from the bolt.
(b) Using a bolt having a deformable nose end allowing a solid ring to be slipped onto the bolt with the tabs engaging the slots and then deforming the nose end to create an abutment which prevents the ring from disengaging. This type of design is limited by the narrow selection of deformable bolt materials and requires a somewhat bulky installation tool needing precise adjustments to prevent over-distorting the bolt. U.S. Pat. No. 4,665,658 to Gulistan is an example of this technique. As disclosed in this patent, the threaded end of the fastener, or bolt, has a hole in it so that after the retaining ring, or washer, is applied to the bolt via the slots formed thereon, the outer end thereof is formed by a hand tool and bent outwardly to a slight extent to close the slot end and thus prevent the washer from being removed from the bolt.
(c) Using a solid ring which was pushed or "shoehorned" over the screw nose, deflecting the tabs or stretching the ring until it snapped into engagement with the bolt slots. The disadvantage of this method lies in the small amount of "springback" inherent to solid rings creating a "set" in the ring shape resulting, in many cases, in insufficient slot engagement. The device described in the aforementioned U.S. Pat. No. 3,294,140 is one example of this technique.
(d) Using a knurled, press-fit plug fitted into a hole located in the bolt nose to captivate the retaining ring to the bolt's longitudinal slots. The plug contains a flange abutment which captivates the ring on the bolt.
Other techniques for captivating the bolt on the panel include those disclosed in U.S. Pat. No. 3,394,747 to Duffy wherein the ring is screwed or pushed onto the stud threads and then crimped; U.S. Pat. Nos. 4,723,881 and 4,865,500 to Duran wherein a ring is deformed from its original shape by crimping and captivated to the outside of an internally threaded bolt by means of a secondary, split ring which is installed onto the nose area of the bolt creating an abutment which prevents the primary, solid rings form falling off; U.S. Pat. No. 2,949,143 to Shur wherein the ring is installed into a housing which is mounted into a panel hole, the housing, by means of a second, surrounding ring, captivating the bolt assembly to the panel; and U.S. Pat. No. 2,492,115 to Crowther wherein the ring is threaded or pushed onto the bolt until it passes the bolt threads and grips an unthreaded portion of the bolt shank, the ring internal portion deforming elastically during installation over the bolt threads and then returning to its original shape to grip unthreaded shank.
U.S. Pat. Nos. 3,561,093 and R.27,978 to Gulistan disclose push-pull tools for pulling on a bolt while pushing upwardly on a housing skirt, thereby outwardly flaring the housing which contains the bolt, the outward flaring of the housing skirt onto the base of a panel captivating the bolt assembly to the panel.
In those techniques requiring a separate installation tool to install the ring on the bolt slots, it is difficult to visually align the tool with the bolt slots for the installation, thus increasing the installation time and the labor costs associated therewith.
What is thus desired is to provide a method for providing a captive panel fastener which utilizes a solid ring retainer, the bolt itself not being deformed during the installation process, and tooling which enables the user to rapidly align and install the ring on the bolt.