Shielded Cable Terminal Assembly

A terminal assembly configured to terminate the shield of a shielded cable having an inner conductor, an inner insulator surrounding the inner conductor, an outer conductor forming a shield surrounding the inner insulator, and an outer insulator surrounding the outer conductor. The terminal assembly includes a generally cylindrical outer ferrule formed of a conductive material and a generally cylindrical inner ferrule formed of a resilient compressible dielectric material. At least a portion of the inner ferrule is disposed within the outer ferrule and a portion of the shielded cable is disposed within the inner ferrule. A portion of the outer conductor is disposed intermediate the inner and outer ferrules and is in intimate contact therewith.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a terminal assembly for an electrically shielded wire cable, particularly a terminal assembly having a resiliently compressible inner ferrule.

BACKGROUND OF THE INVENTION

Braided shields of shielded cables are currently terminated by placing the braids of the shield between a metal inner and outer ferrule before crimping. An example of a terminal assembly suing these ferrules is shown inFIGS. 1A-1D. The outer insulation of the cable112is first removed to expose the braided shield118and the braids of the shield are then flared and a metallic tubular inner ferrule122is placed between the braids118and the inner insulation114of the shielded cable112(seeFIG. 1A). A metallic tubular outer ferrule132is placed over the braided shield118and inner ferrule122(seeFIG. 1B) and then crimped136to secure the outer ferrule132to shielded cable112(seeFIGS. 1C and 1D).

The difference between the inner diameter of the outer ferrule132and the outer diameter of the inner ferrule122is typically about 1 millimeter. Thick inner ferrules can degrade the strength of the crimp possibly reducing pull off force and increasing shield to outer ferrule electrical resistance. Thin inner ferrules can rupture during crimping. Rupture of the inner ferrule122could cause undesirable electrical contact and shorting of the inner conductor114and the braided shield118. Therefore, the inner and outer ferrule diameters must be carefully matched and different cable sizes and applications require different sized inner and outer ferrules. The inner and outer ferrules are formed by either deep draw stamping or machining; both of these manufacturing methods are relatively expensive. These inner and outer ferrule sizes may differ only slightly for different shielded cables which may make it difficult to visually distinguish between different sized inner or outer ferrules. Applying markings, such as color coding, may be used to help identify different ferrules. However, applying these markings is an additional manufacturing process that undesirably increases ferrule manufacturing time and cost. Therefore, a reliable ferrule assembly that can easily accommodate different cable sizes remains desired.

BRIEF SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a terminal assembly is provided. The terminal assembly is configured to terminate a shielded cable having an inner conductor, an inner insulator surrounding the inner conductor, an outer conductor surrounding the inner insulator, and an outer insulator surrounding the outer conductor. terminal assembly includes a generally cylindrical outer ferrule formed of a conductive material and a generally cylindrical inner ferrule formed of a resilient compressible dielectric material. At least a portion of the inner ferrule is disposed within the outer ferrule and a portion of the shielded cable is disposed within the inner ferrule. A portion of the outer conductor is disposed intermediate the inner and outer ferrules and is in intimate contact therewith. As used herein, generally cylindrical means that the inner and outer ferrules are cylindrical within the typical manufacturing tolerances and variations of the methods used to form the ferrules.

The resilient compressible dielectric material may be a silicone-based material. The resilient compressible dielectric material may have a Shore A durometer hardness between 30 and 80. The inner ferrule may have a generally constant outside diameter. The outer ferrule may be crimped to the inner ferrule and the inner ferrule may be deformed by the outer ferrule. An inner surface of the outer ferrule may define a projection configured to contact and indent the outer conductor and the inner ferrule. The inner ferrule may define a circumferential rib protruding beyond the outer ferrule. The inner ferrule may define a plurality of circumferential ribs protruding beyond the outer ferrule and the outer diameter of each circumferential rib may be substantially uniform. The plurality of circumferential ribs may be resilient. As used herein, substantially uniform means that the outer diameter of each circumferential rib is ±5% the same diameter of every other circumferential rib in the plurality of circumferential ribs.

In accordance with another embodiment, a terminal assembly terminating a shielded cable wherein a metallic inner wire cable covered by an inner insulator is sheathed by braided metallic wires on an outer periphery of the inner insulator and further covered by an outer insulator surrounding the braided metallic wires and wherein the braided metallic wires are exposed at one end of the shielded cable is provided. The terminal assembly includes a generally cylindrical inner ferrule formed of a resilient compressible dielectric material inserted between the outer insulator and the exposed braided metallic wires bent back over the inner ferrule and a generally cylindrical outer ferrule formed of a conductive material crimped over the exposed braided metallic wires. At least a portion of the inner ferrule is disposed within the outer ferrule and wherein a portion of the exposed braided metallic wires are disposed intermediate the inner and outer ferrules and is in intimate contact therewith.

The resilient compressible dielectric material may be a silicone-based material. The resilient compressible dielectric material may have a Shore A durometer hardness between 30 and 80. The inner ferrule may have a generally constant outside diameter. An inner surface of the outer ferrule may define a projection configured to contact and indent the outer conductor and the inner ferrule. The inner ferrule may define a circumferential rib protruding beyond the outer ferrule. The inner ferrule may define a plurality of circumferential ribs protruding beyond the outer ferrule and the outer diameter of each circumferential rib may be substantially uniform. The plurality of circumferential ribs may be resilient.

DETAILED DESCRIPTION OF THE INVENTION

Presented herein is a terminal assembly including features configured to terminate a shield of a shielded cable having an inner conductor, an inner insulator surrounding the inner conductor, an outer conductor surrounding the inner insulator, and an outer insulator surrounding the outer conductor. The terminal assembly includes a generally cylindrical outer ferrule that is formed of a conductive material and a generally cylindrical inner ferrule that s formed of a resilient compressible dielectric material. The inner ferrule is placed over an end portion of the shielded cable. A portion of the outer insulator is removed and an exposed portion of the outer conductor is placed over the inner ferrule and the outer ferrule is then placed over the inner ferrule. The outer ferrule is then crimped to retain the terminal assembly to the shielded cable, plastically deforming the outer ferrule and elastically deforming the inner ferrule. The exposed portion of the outer conductor is disposed intermediate the inner and outer ferrules and is in intimate contact therewith.

Reference numbers for similar features in the drawings and the description of the prior art and the various embodiments of the invention share the last two digits.

By referring now to the drawings, embodiments of the invention will be explained below. It will be appreciated that the terminal assemblies shown inFIGS. 1A-1DandFIG. 8do not fall within the scope of the claims but are provided here as they clarify the scope of the invention.

FIGS. 2-7show a non-limiting example of a terminal assembly10configured to terminate a shield of a shielded cable12and a method of forming such a terminal assembly10. As shown inFIG. 2, the shielded cable12includes an inner conductor14comprising metallic core wires, a first or inner insulator16surrounding the inner conductor14, an outer conductor18formed of braided metallic wires which sheathe the inner insulator16, and a second or outer insulator20that covers the outer conductor18. A sleeve-like body or generally cylindrical inner ferrule22having an inner diameter sufficient to receive the shielded cable12is slid over an end portion of the shielded cable12in a direction shown by arrow24.

As shown inFIG. 7, the outer surface26of the inner ferule22has a generally uniform outer diameter. Leading and trailing edges28,30of the inner ferrule22may be beveled. The inner ferrule22is formed of a resilient compressible dielectric material. The resilient compressible dielectric material is an elastomeric material having a Shore A durometer hardness between 30 and 80, such as silicone-based material. The inner ferrule22merely serves to support the outer conductor18and does not need to electrically communicate with the outer conductor18. The inner ferrule22may be formed by an injection molding process.

Although the inner ferrule22is formed into a complete cylindrical body in the embodiment shown inFIGS. 2-7, the inner ferrule may alternatively comprise a pair of half parts divided axially or may be provided with a slit extending axially since the inner ferrule could be brought into a complete cylinder when it is assembled on the shielded cable and may simplify the step of mounting the inner ferrule to the shielded cable.

Looking now atFIG. 3, the shielded cable12is stripped at one end so that at least a portion of the outer insulator20is removed exposing the braided wires of the outer conductor18. Then, as shown inFIG. 4, the braided wires of the outer conductor18are flared and pulled back over the inner ferrule22covering at least a portion of the outer surface26of the inner ferrule22.

Next, as shown inFIG. 5, another sleeve-like body or generally cylindrical outer ferrule32having an inner diameter sufficient to receive the inner ferrule22and braided wires of the outer conductor18coving the inner ferrule22is slid over at least a portion of the inner ferrule22in the direction shown by arrow24. The outer ferrule32is formed of a conductive metallic material, such as a tin plated copper alloy. The outer ferrule32may be formed by a deep draw stamping process or a machining process. At least one open end34of the outer ferrule32has an opening as large as the inner diameter of the outer ferrule32.

Finally, as shown inFIG. 6, the outer ferrule32is crimped, i.e. indentations36are formed in the outer ferrule32, thereby plastically deforming the outer ferrule32and elastically deforming the inner ferrule22in order to retain the terminal assembly10to the shielded cable12and putting the outer ferrule32and inner ferrule22in intimate contact with the outer conductor18therebetween. The outer ferrule32may then be electrically connected to an electrical ground (not shown) such as a conductive casing.

FIG. 8illustrates an example of a cross section of a crimped terminal assembly110having a metallic outer ferrule132and a metallic inner ferrule122according to the prior art. The outer ferrule132and the inner ferrule122are both plastically deformed during the crimping process. As can be seen, there are voids125between inner ferrule122and the outer ferrule132that may reduce the pull off force needed to pull the terminal assembly110off of the shielded cable and could allow water and other contaminants to enter the terminal assembly110causing corrosion that could increase electrical resistance between the outer conductor118and the outer ferrule132and further reduce pull off force. In addition, there are a number of the strands of the braided wires of the outer conductor118that are not in contact with the outer ferrule132which may further increase electrical resistance between the outer conductor118and the outer ferrule132.

FIG. 9illustrates a cross section of the terminal assembly10shown inFIGS. 2-7and described above. In contrast to the terminal assembly10shown inFIG. 8, the number and size of voids is greatly reduced. Further, there are fewer strands of the strands of the braided wires of the outer conductor18that are not in contact with the outer ferrule32.

Through testing, the terminal assembly110ofFIG. 8has been found to have a pull off force of about 560 newtons while the terminal assembly10ofFIG. 9has been found to have a pull off force of about 690 newtons, meeting or exceeding the pull off force performance of terminal assembly110. Without subscribing to any particular theory of operation, the elastic deformation of the inner ferrule22provides the reduction of voids between the inner and outer ferrule32and may contribute to improved pull off force performance compared with the prior art terminal assembly110. In addition, testing by the inventors has found that the resistance between the outer conductor18and the outer ferrule32of the terminal assembly10is comparable to the terminal assembly110.

It may be appreciated that the terminal assembly10has a reduced likelihood of short circuit between the outer ferrule32or outer conductor18and the inner conductor14since the inner ferrule22is also an insulating body rather than a conductive body as seen in prior art terminal assemblies, e.g.FIG. 8.

In addition, it may be recognized that an outer ferrule32having one specific inner diameter may be used with multiple shielded cable12diameters by merely varying the inner and outer diameter of the resilient inner ferrule22, since it is no longer necessary to maintain a difference between the inner diameter of the outer ferrule32and the outer diameter of a metallic inner ferrule22of about 1 millimeter to avoid issues of thick inner ferrules can degrade the strength of the crimp and thin inner ferrules can rupture during crimping described in the BACKGROUND OF THE INVENTION section above. This will reduce the number of different outer ferrule designs and part numbers required to accommodate different cable sizes. The inner ferrule22can easily be color coded to identify different inner ferrule22sizes by adding a colorant to the elastomeric material prior to molding the inner ferrule22.

FIG. 10illustrates an alternative embodiment of the terminal assembly210wherein the inner ferrule222includes an anti-creepage feature240in the form of an electrically insulative rib protruding beyond the outer ferrule232intermediate the outer ferrule232and a terminal (not shown) connected to the inner conductor214. This feature may allow smaller connector package size for high voltage application where creepage between the inner connector and the outer ferrule232is a concern.

FIG. 11illustrates another alternative embodiment of the terminal assembly310wherein the inner ferrule322includes an anti-vibration feature342in the form of a number of resilient ribs protruding beyond the outer ferrule332intermediate the outer ferrule332and a terminal (not shown) connected to the inner conductor314to dampen terminal vibration.

FIG. 12illustrates yet another alternative embodiment of the terminal assembly410wherein the inner ferrule422includes sealing feature444in the form of a number of resilient ribs protruding beyond the outer ferrule432aft of the outer ferrule432that are configured to contact an inner surface of housing (not shown).

While the examples of the terminal assembly presented above illustrate a shielded cable having a braided outer conductor, other embodiments of the invention may be envision that are used with a shielded cable having foil or conductive film outer conductors.

Accordingly a terminal assembly10having an inner ferrule22formed of a resilient compressible dielectric material is provided. The terminal assembly10provides a cost advantage over prior art terminal assemblies110by replacing deep drawn or machined inner ferrules with a molded inner ferrule that can be produced inexpensively. One size inner ferrule may be molded to match required cable size which eliminates the need for multiple sizes of inner ferrules. The terminal assembly10may also allow some applications to use one outer ferrule size for multiple cable sizes. The inner ferrule22may be common to multiple applications. The inner ferrule22may be colored to provide visual differentiation between various sizes. The inner ferrule22provides increased insulation protection for the inner conductor and decrease the risk of piercing through the insulation of the core conductor. The inner ferrule222may incorporate features to reduce distance needed to avoid creepage in high voltage applications, allowing the outer ferrule to located closer to a terminal attached to the inner conductor. The inner ferrule322may incorporate features to provide additional terminal dampening for high vibration applications. The inner ferrule422may incorporate features to provide an integral cable seal. The terminal assembly10also provides more stands of outer conductor in contact with outer ferrule32and provides fewer voids between the inner ferrule and the outer ferrule32. The terminal assembly10also meets or exceeds the pull off force compared to the prior art terminal assembly110.

While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. Moreover, the use of the terms first, second, etc. does not denote any order of importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.