Patent Application
20070117448
1. Field of the Invention
The present invention relates to electrical connector strain relief mechanisms and more particularly to the use of indexing teeth for positive engagement between accessory teeth in a connector and a strain relief cable clamp employing an coupling ring with self locking engagement mechanisms.
2. Description of the Related Art
The assembly of a strain relief cable clamp or “backshell” which has a self-locking mechanism (for vibration resistance properties) and rear accessory teeth as defined in Military standard MS3155 onto an electrical connector having the same MS3155 accessory teeth can result in binding which precludes proper assembly of the backshell and connector. The backshell includes a self locking device which consists of two arch shaped spring fingers, each having a detent positioned at opposite ends of the arch. The two spring fingers are installed longitudinally and circumferenctially across from each other in a formed 360° slot on the interior surface of the coupling ring. The backshell body includes accessory teeth on its proximal end and spaced serrations with predetermined spacing on the circumferential periphery of the body located at the root of the teeth to engage the self locking devices. The coupling ring is provided with three inspection holes spaced at 120° around its periphery. The accessory teeth on the electrical connector are positioned on the shell or body opposite the connector engagement face.
When the backshell is coupled onto an electrical connector, the self-aligning movement or coupling of the two components is impeded when both sets of accessory teeth are at a peak-to-peak condition which often results in “binding”, creating a false coupled backshell and connector. This condition exists when the spring fingers detents on the self-locking devices on the backshell are locked onto the serrations without proper seating of the accessory teeth. In this condition, the approximately 0.035 to 0.04 radius on the peak of each interfacing tooth coupled with the large number of accessory teeth prevents any sliding action from occurring. The number of teeth can be from a minimum of twelve (12) to a maximum of fifty four (54). Applying torque to the backshell will not resolve the “binding” condition and the interfacing accessory teeth are not engaged or coupled. Therefore, the backshell is physically loose negating the desired vibration resistant properties which are non-existent without a complete mating interface of the accessory teeth. This condition often directly leads to finding non-compliance on the bonding and grounding requirements in complex systems such as aircraft.
It is therefore desirable to provide an arrangement to eliminate the problematic peak-to-peak condition during assembly of the strain relief cable clamp onto an electrical connector. It is further desirable to ensure that the ElectroMagnetic Interference/Radio Frequency Interference (EMI/RFI) performance of the backshell is not compromised or dependent on its assembly process onto the electrical connector. Additionally, it is desirable to allow self-locking devices on the backshell to not interfere with the coupling or engagement of the interfacing accessory teeth between backshell and electrical connector. It is still further desirable to eliminate the need for the inspection holes on the backshell coupling ring.
A self-aligning coupling apparatus employing the present invention incorporates a first connecting element having a body with a first set of accessory teeth and a second connecting element having a body with a second set of accessory teeth for engagement of the first set and a coupling ring which joins the first and second element. The first set of accessory teeth includes at least one indexing tooth having an apex angle less than an apex angle of the remaining teeth of the first set, the at least one indexing tooth further has a height greater than the remaining teeth of the first set. The second set of accessory teeth is equal in number to the first set and has an apex angle complementing the apex angle of the remaining teeth of the first set. The second set of accessory teeth have canals intermediate the teeth to receive the at least one indexing tooth upon joining of the first and second element by the interconnecting coupling.
In exemplary embodiments, the first set of accessory teeth incorporates two or three indexing teeth spaced around the circumference of the first connecting element body. The indexing teeth have an apex angle of approximately 30° and are significantly longer than the remaining accessory teeth in the set.
These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
a is an exploded perspective view, made in accordance with prior art, depicting self-locking, strain relief cable clamp or backshell and electrical connector having MS3155 accessory teeth;
b is a detailed view of the self-locking elements of the assembly of
c is a detailed view of the serrations and accessory teeth of the backshell;
a is a side sectional view of the assembled backshell and electrical connector illustrating the peak-to-peak accessory teeth engagement;
b is a detailed perspective sectional view of the self-locking devices with the spring fingers detent locked in the receiving serrations;
a is a perspective partial sectional view of the modified accessory teeth of a first embodiment of the present invention;
b is a detailed side section view showing one of two indexing accessory teeth 180° apart on the connector have a 30° internal angle on the triangular shaped tooth and an 0.01 to 0.015 tooth peak radius on both backshell and connector accessory teeth;
b is a detailed side view showing the canal located at the root of each tooth on the backshell accessory teeth;
a is a sectional side view of a properly coupled electrical connector and backshell employing the present invention; and
b is a magnified partial view of the details of the engagement of the accessory teeth with the indexing tooth received in a canal.
To better understand the embodiment of the invention disclosed herein,
An exemplary embodiment of the invention is shown in
To better understand the overall assembly and demonstrate the effectiveness of the modified MS3155 accessory teeth, the following detailed explanation of the coupling action between electrical connector 10 and backshell 12 is provided. With reference to Fig. 4a, the internal thread of backshell coupling ring 14 engages the external thread of electrical connector 10 and a shoulder 42 on the body of the backshell and with each clockwise rotational movement pulls the interfacing accessory teeth 26 and 28 toward each other. Having initial contact created by only two or three indexing teeth 32 instead of the full compliment of the accessory teeth which depending on the electrical connector and backshell shell size may number 12 to 54 in various configurations, lessens the number of teeth potentially at the previously described peak-to-peak condition. Additionally, the higher contact angle created by the 30° apex angle in the indexing teeth and the smaller radius on the accessory teeth reduces the potential for binding of an indexing tooth on an opposing accessory tooth and deflects the indexing teeth from the apex of the opposing accessory teeth into the adjacent canals. Thus the rotational force being applied at the backshell coupling ring overcomes the ‘binding’ between any peak-to-peak index teeth and opposing accessory teeth and the slipping interface between the initially contacting indexing teeth the opposing accessory teeth causes a relative rotation between the connector and the backshell enhancing self alignment of the sets of accessory teeth. Also, it is understood the 0.01-0.015 in radius at the peak of the accessory teeth enhances the sliding action between interfacing teeth allowing accessory teeth 26 and 28 to bottom as shown in
The assured engagement of the accessory teeth allows the elimination of the three inspection holes which perforate the “backshell coupling ring and can be a source for fluids, grime/dust, etc. to enter the mated connector and backshell. Eliminating the perforations avoids the corrosion/contamination that will significantly degrade the Electromagnetic Interference/Radio Frequency Interference (EMI/RFI) integrity required by applications in which the presently disclosed invention may be employed such as aircraft systems. An unperforated ring is therefore highly desirable. It should be noted that the backshell assembly onto an electrical connector is now a single performance functionality with respect to modern aircraft quality inspection. It is understood that bonding and grounding is accomplished through the shielded cable to the backshell to the electrical connector to the airplane structure in an aircraft application. The EME requirement has become more stringent and critical on newer airplanes. The present invention therefore provides lower assembly and repair cost for aircraft and other complex systems.
Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.
