Backshell connection

Using a new lock coupling handling mechanism prevents thread decoupling under conditions of extreme vibration

Loose connections have always been quoted by airline companies as a major cause of propulsion related connector problems. Vibration, line replacement, unit harness connector incompatibility, and access limitations are the major cause of problems. Many different ways have been offered to solve this issue, with varying degrees of success.

The extreme vibration found near the engine core causes self locking connectors to loosen, exposing the connector to contaminates and causing contact fretting. The design of the connector bracket has also occasionally caused such vibrations to be amplified.

There have been a number of devices invented where the nut on a connector or backshell cannot come undone. Recent self-locking devices utilised differential torque locking with a spring click mechanism.

Unfortunately, there are two main difficulties with this technology. Firstly, the `torque to tighten’ is so high that it is difficult to establish if the nut is fully tightened or merely stiff to operate. As this method necessitates `hand operation’, it is also difficult to tighten the nuts in awkward, space restricted environments. Secondly, there is a severe problem in engaging the backshell teeth to the teeth of the connector in such a way that they do not `stand off’ from one another. As these teeth meet at their lips, they tend to harden into that position causing both mechanical stress and loss of feel to the operator for the device.

This, in turn, gives a high electrical resistance which may deteriorate after vibration. This problem has led to the introduction of an inspection viewing hole to examine the teeth. However, it is not possible to gain access for wiring in many aircraft installations.

According to Icore International, a new backshell connector overcomes these problems by using a new concept – a lock coupling handling mechanism that allows both a greater degree of operator `feel’ and a non-friction, stress free locking of the connector into the backshell. The nut stays free until tightened and then another movement locks it in such a way that it cannot come undone without being tampered with.

The system has been designed to eliminate `lock wiring’ and prevent thread decoupling under conditions of extreme vibration. Geared to suit all circular connectors with rear accessory `locking teeth’, it operates with stainless steel, aluminium and all conductive or non-conductive finishes.

The high-temperature, lightweight `one-click’ lock ring of Optilock allows simple assembly onto connector accessory threads using a conventional style nut. Once in position, the simple action of sliding the lock ring back from the connector until the blue safe lock band comes into view ensures that no rotational movement of the engaged threads is possible. When required, the ring (a high temperatue metallic construction) can be manually moved forward to disengage the locking mechanism. Electrical continuity is maintained even under the extreme vibration of 40g or more.

Retaining all the advantages of traditional spin coupling nuts, the new product eliminates the need to crosslock connectors/backshells using conventional locking wire, saving installation time and cost. Bulkier and heavier differential torque solutions (with associated mechanical parts which may wear out) are now unnecessary in many applications.

The latest version of the connector uses grounding fingers to ensure full electrical continuity and better contact resistance between the metal components and the backshell. This innovative development is advantageous in high vibration applications.

Contact resistance through a backshell and connector are commonly lost through the teeth of the locking system; through nuts working loose, even to a slight degree. But the new copper beryllium grounding fingers now effectively fill the gap between backshell and connector and firmly lock the device. Even when the nut is disengaged, the bridge contact is still in place and resistance is maintained.

It is claimed that the device goes beyond the usual concept of grounding fingers under `spring pressure’ (which usually results in broken fingers over a period of time). A low level of stress concentration has been designed into the device along with extra protection to ensure that the effects of vibration are kept to a minimum.

Figure 1: The Optilock backshell connector uses a lock coupling handling mechanism. The nut stays free until tightened and then another movement locks it shut in such a way that it cannot come undone without being tampered with

Figure 2: The lock ring is shown in both the locked and unlocked positions

Figure 3: Optilock connector attachments are combined with a flexible conduit as an alternative to traditional heavy metal elbows

{{Icore InternationalTel: Slough (01753) 574134Enter 460}}