GB2180028A

GB2180028A - Triple redundant shear bolt

Info

Publication number: GB2180028A
Application number: GB08621190A
Authority: GB
Inventors: Robert B Silcox
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1985-09-09
Filing date: 1986-09-02
Publication date: 1987-03-18
Also published as: GB2180028B; GB8621190D0; CN1005497B; CN86105932A; AU582465B2; AU6252586A; JPS6262012A; DE3630002A1

Abstract

A bolt 10 is provided with a radial, spring-loaded pawl 26, and an associated nut 24 is provided with cooperating detents on its inner diameter that cooperate with the pawl 26 so that the nut 24 does not back off the bolt 10. The nut 24 is also castellated for insertion of a cotter pin 21 through the bolt 10 so that the nut 24 is further restrained from backing off. In the event that the nut 24 backs off, the pawl 26 prevents the bolt 10 from pulling out of a close tolerance hole, such as a rod end fitting. <IMAGE>

Description

SPECIFICATION Triple redundant shear bolt Technical field of the invention The invention relates to fasteners and, more part icularly, to those with positive lock featu res.

Background of the invention In aircraftcontrol system applications,a nut backing off, and subsequent loss of the bolt, is not acceptable. Therefore, it is typical to provide a hole in the bolt shank, nearthe end of the threads, so that a cot- ter pin can be inserted through a castellated (slotted) nut in order to prevent the nut from backing off.

Failuretoinsertthecotterpin during maintenance can create a safety hazard. Therefore, it is known to provide self-retaining bolts. These bolts have an axial, spring-loaded cam-plunger acting on a ball protruding from the shank (much like the renowned Sears' socket wrench). When the plunger is dep ressed, the bal I can move radially within the shank so that the bolt can be inserted through a closetolerance hole, such as the hole in a control rod end fitting. When the plunger is released, the ball protrudes beyond the shank on the other side ofthe fitting from the bolt head sothatthe ball preventstheboltfrom coming out of the hole if the nut backs off. However, the hollow shank required to accommodate the plunger creates a noninspectable, corrosion-prone bolt.

This is especially pertinent in a salt water spray environment.

Disclosure ofthe invention It is an object ofthis invention to provide a selfretaining bolt without a hollow shank.

According to the invention a bolt is provided with a radial, spring-loaded pawl, and an associated nut is provided with detents on its inner diameter that cooperate with the pawl so that the nut does not back offthe bolt. The nut is also castellated for insertion of a cotter pin through the bolt so that the nut is further restrained from backing off. In the event that the nut backs off, the pawl prevents the bolt from pulling out of a close tolerance hole, such as a rod end fitting.

Other objects, features and advantages of the in vention will become apparent in light of the follow- ing description thereof.

Brief description ofthe drawings Figure lisa side view ofthe bolt of this invention.

Figure2 is a view of the bolt taken through the section 2-2 of Figure 1, including a nut.

Figure 3 is three orthographic projection views of the pawl for the bolt ofthis invention.

Best mod forcarrying out the invention Figure 1 shows the bolt 10 ofthis invention. The bolt 10 comprises a head 12 and a shank 14. A portion 16 of the shank 14 opposite the head 12 is threaded to receive a nut. Near the tip end 18 oftheshank 14a hole 20 is provided perpendicular to the bolt axis for receiving a cotter pin 21. Just beyond the bolt head end of the threaded portion 16 another hole 22 is provided in the shank 14 perpendicularto the bolt axis, preferably parallel to the cotter pin hole 20.

The hole 22 is best viewed in Figure 2, which shows a section of the bolt 10, and associated nut 24 taken through the section 2-2 of Figure 1. The hole 22 is "stepped" to receive and retain a pawl 26. The pawl 26 has a tip 27, a head 28, and a base 29. The head 28 is of a first cross-sectional dimension corresponding to a portion 30 of the hole 22, and the base 29 is of a second cross-sectional dimension, largerthan the first dimension, corresponding to a portion 34 ofthe hole 22. Details ofthe pawl 26 are shown in Figure 3.

The junction of the hole portions 30 and 34defines the aforementioned "step" so that the pawl may be inserted "tip first" into the portion 34 of the hole 22, perpendicularly through the bolt 10 until further in sertion is prevented by the step. At this point, the tip of the pawl protrudes beyond the shank of the bolt.

A spring 36 is inserted into the hole portion 34 be hind the base of the pawl so as to exert force thereon that causes the pawl tip to protrude radiallyfromthe bolt shank. The spring 36 is retained within the hole portion 34 of the bolt shank by a plug 38 that is pressfitted and staked within the hole 22, opposite the pawl head 28.

Figure3showsthreeviewsofthepawl26. Inan end view (A), it is apparent that the head 28 ofthe pawl 26 is essentially square in cross section. Thus the portion 30 of the hole 22 is square to receive the pawl head 28 and prevent its rotation. In a first side view (B), corresponding to the perspective of Figure 2, it is apparent that two opposite sides of the pawl tip 27 are fully radiused. In a second side view (C), taken perpendicularto the bolt axis and the hole 22 axis, it is apparent that the upper and lower surfaces ofthe pawltip27aresimplyflat,and inalignmentwiththe square pawl head surfaces.

Figure 1 shows a rod end fitting 40/clevis 41 receiving the bolt 10. To insertthe bolt 10 into a the rod end fitting 40, the pawl is depressed manually into the shank during initial insertion. During further inser- tion, the pawl is caused to be held within the shank by the inside surface 42 of the fitting. Upon full insertion of the bolt 10 into the fitting 40, the pawl is no longer within the fitting and its tip protrudes from the bolt shank as urged by the spring 36. The flat uppersur- face ofthe pawl tip 27 retains the bolt within the fitting. It is importantthatthe pawl head and applicable hole portions be shaped (square in this illustration) to preventrntarion ofthe pawl within the bolt.This restriction ofthe pawl allows a flat surface of its tip portion to contact and bear against the surface ofthe parts to be retained (the fitting in this illustration) in the event of loss of the nut. The extended pawl will act as a stop and perform its retention function.

Returning to Figure 2, it will be noted that the inside diameter of the bolt-head-facing portion 43 of the nut 24 is provided with six equally spaced radiused detents 44, corresponding to the radiused pawl head and sized so asto receive the protruding tip of the extended pawl head. The pawl tip prevents a rounded surface so as to allow its extension into and out of the nut detents as the nut is advanced toward contact with the fitting. In the absence of applying torque (wrenching force) to the nut the extended pawl wiil prevent the nut from backing off.The por tion 46 of the nut awayfrom the bolt head is provided with conventional casteliations (slots) 48 aligned with the hole 20 and insertion of the cotter pin 21 therethrough as an additional means of preventing the nut from backing offthe bolt. The parallel alignment ofthe detents and nut castellations provide for full extension ofthe spring biased pawl into a detent simultaneously with the retention action of the cotter pin. It is desirable that the pawl be already in an action position for retention in the event of loss ofthe cotter pin. In the event of a pawl jam, it is desirable for the pawl to be in its extended position in the detent ratherthan in a compressed position between detents.

Thus, the "triple-redu ndancy" of the bolt ofthis invention resides in the cotter pin preventing nut backoff, the pawl preventing nut backoff and the pawl providing self-retention for the bolt in the event of nut backoff.

Numerous deviations and alternatives are available to the designers within the teachings ofthis invention. For example, while a drilled stopper hole has been described and illustrated, it may be economically desirableto create a step by insertion of a bushing in one end of a constant diameter hole in the bolt shank. Likewise, in place of separate elements comprising a pawl, spring and plug, it may be desirable to utilize an assembly comprising a tubular insert. Further, othershapesthan square may be used for prevention of pawl rotation. Also, while the aforementioned description mentions use ofthis invention for close tolerance hole applications it should be recognized that in certain very close dimensioned fits between boltshankandfittings, it may be possibleto use a spherical shaped pawl tip and attendant circular pawl head, which can be allowed to rotate. The complexity ofthe pawl shape is a function of the application and should not be considered a limitation of this invention.

The perpendicular hole 22 ofthis invention provides superior corrosion resistance to the longitudinal hole ofthe prior art, especially in light of the nut 24 completely covering the hole 22 when assembled.

I claim as my invention:

Claims

1. Afastenercomprising: a bolt having a head and a shank, a portion ofthe shank away from the head being threaded; a first hole provided through the shank per pendicularto the bolt axis including a first hole portion of a first cross-sectional dimension extending to the surface ofthe shank and a second hole portion of a second cross-sectional dimension greater than the first hole portion extending to the diametrically opposed surface ofthe shank, wherein the junction of the first hole portion and the second hole portion forms a step; a pawl having a head corresponding in end cross section to the first dimension disposed within the first hole portion, having a tip protruding outsidethe surface ofthe shank, and having a base corresponding in end cross-section to the second dimension disposed within the second hole portion;; a spring disposed behind the base of the pawl so as to exert a pawl-protruding force on the pawl; a plug fixed within the diametrically opposed surface of the shank in the second hole portion to retain the spring within the shank, and a nut provided with detents on its inner diameter corresponding to and receiving the protruding pawl tip so that nut backoff is resisted by cooperation between the pawl and the detents.

2. Afasteneraccording to claim 1,furthercom- prising: a second hole provided through the threaded portion ofthe bolt perpendicular to the bolt axis; and castellations on the nut for receiving a cotter pin through the second hole so that nut backoff is further resisted by cooperation between the second hole, castellations, and the cotter pin.

3. Afastenerforinsertionthrough a closetoler- ance hole in a fitting, comprising the fastener of claim 1 wherein the first hole is disposed appropriately along the length ofthe shank so thatthe pawl is on the opposite side of the fitting from the bolt head and restricts the boltfrom pulling outofthe fitting.

4. Afasteneraccordingto claim 1 wherein the pawl head is square in end cross section and the two opposite sides of the pawl tip are fully radiused so that insertion ofthe nut over the pawl isfacilitated thereby.

5. Afastener according to claim 4wherein the upper and lower surfaces of the pawl tip are flat.

6. Afastener according to claim 4 wherein the first hole is square in cross section to receive and prevent the pawl from rotating.