Patent Publication Number: US-2009236119-A1

Title: Finned jacket with core wrap for use in lan cables

Description:
This application claims the benefit of U.S. Provisional Application No. 61/037,900, filed Mar. 19, 2008, the entire contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to communication cables. More particularly, the present invention relates to a twisted pair cable having a jacket with projections on an inner wall to provide air channels around a core of the twisted wire pairs, and to a structure to permit maximization of the air channel dimensions. 
     2. Description of the Related Art 
     Jackets with projections or fins on an inner wall of the jacket are known in the prior art. For example, U.S. Pat. No. 3,894,172, U.S. Pat. No. 5,796,046, U.S. Pat. No. 7,238,886, and U.S. publication 2005/0133246, each of which is herein incorporated by reference, show a cable having internal fins or projections. 
     SUMMARY OF THE INVENTION 
     The applicant has appreciated one or more drawbacks of the cable designs of the prior art. 
     First, there is a general goal in the design to maximize the air channel size and minimize the fin size. The reason for the general goal is to include as much air as possible in the immediate vicinity of the cable core (twisted wire pairs—possibly with a tape or star separator) and to include as little jacket material (e.g., fins) in the immediate vicinity of the cable core. Air has a dielectric constant of approximately 1.0, whereas the jacket material may have a dielectric constant of approximately 2.0-4.0 depending upon the jacket material. For example, polyethylene can have a dielectric constant of 2.3 and FEP can have a dielectric constant of 2.1. Having a generally lower dielectric constant material, e.g., air, nearest to the cable core improves the electrical performance of the cable. 
       FIG. 1  shows a cross sectional view through the finned jacket cable of U.S. publication 2005/0133246. As shown in  FIG. 1 , a cable  10  includes widely spaced fins  11  creating wide air channels  13 . Four twisted wire pairs (A, B, C and D) are located in the cable core.  FIG. 2  is the same as  FIG. 1 , but illustrates in broken lines the intended occupation areas (a, b, c and d) of the four twisted pairs (A, B, C and D), respectively.  FIG. 2  also illustrates in a broken line (e), the intended occupation area of the entire cable core. As can be seen in  FIG. 2 , the intended occupation areas (a, b, c and d) of the four twisted wire pairs (A, B, C and D), and hence the occupation area (e) of the cable core, are not intended to enter into the air channels  13 . 
     One drawback appreciated by the Applicant is that in the quest to expand the channel width, the possibility of a wire of a twisted pair entering an air channel  13  increases. The air channel  13  can be made so wide that one or both wires of a twisted pair A, B, C or D may slightly or fully enter into a channel  13 . This negates the effectiveness of the finned jacket. Once a wire enters the air channel  13 , the wire is closely surrounded by the insulating material of the jacket with the higher dielectric constant. 
     As seen in  FIG. 3 , it is possible for a wire  21  of the twisted pair D to fully enter into an air channel  13 . The wire  21  is then closely adjacent to the jacket material.  FIG. 3  also illustrates a wire  22  of the twisted pair C, which has partially entered into an air channel  13  to be proximate the jacket material. These intrusions into the air channels  13  may occur along the length of the cable  10  at various points and to varying degrees, leading to variations in signal performance along the length of the cable  10  (e.g., impedance variations). 
     The number of intrusions into the air channels  13  along a given length of cable  10  and the extent of the intrusions into the air channels  13  are based upon several factors, primarily including—the size of the air channels  13 , whether or not a core twist is used, if a core twist is used—the core lay length, the number of bends in the cable  10  along its ultimate route, the angular extent of the bend(s) in the route of the cable  10 , the pulling force applied to the cable  10  during installation, and any constant pressure on the cable jacket due to adjacent cables and other objects. 
     Another potential drawback is that over time, contact points (as illustrated by reference numeral  24  in  FIG. 1 ) between the jacket material and the wire&#39;s insulation can form an adherence. This may be due to plasticization, and can depend upon the environmental surrounding, heat and pressure exposures during storage and installation, and aging. The adhesion spots  24  can be troublesome during connector termination, when stripping off the jacket. Also, the adhesion spots  24  could cause impedance variations along a length of the cable  10  and other performance issues. 
     It is an object of the present invention to address one or more of the drawbacks which the Applicant has appreciated in the background art. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus, are not limits of the present invention, and wherein: 
         FIG. 1  is a cross sectional view of a twisted pair cable with four twisted pairs, in accordance with the background art; 
         FIG. 2  is a cross sectional view of the twisted pair cable of  FIG. 1  illustrating the boundaries of the four twisted pairs individually and as a core; 
         FIG. 3  is cross sectional view illustrating potential breaches into air channels by the twisted pairs in the cable of  FIG. 1 ; 
         FIG. 4  is a cross sectional view of a twisted pair cable, in accordance with a first embodiment of the present invention; 
         FIG. 5  is a perspective view of a twisted pair cable, in accordance with a second embodiment of the present invention; 
         FIG. 6  is a cross sectional view taken along line VI-VI in  FIG. 5 ; 
         FIG. 7  is a perspective view of a twisted pair cable, in accordance with a third embodiment of the present invention; 
         FIG. 8  is a perspective view of a twisted pair cable, in accordance with a fourth embodiment of the present invention; and 
         FIG. 9  is a cross sectional view taken along line IX-IX in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     The present invention now is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Like numbers refer to like elements throughout. In the figures, the thickness of certain lines, layers, components, elements or features may be exaggerated for clarity. Broken lines illustrate optional features or operations unless specified otherwise. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well-known functions or constructions may not be described in detail for brevity and/or clarity. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, phrases such as “between X and Y” and “between about X and Y” should be interpreted to include X and Y. As used herein, phrases such as “between about X and Y” mean “between about X and about Y.” As used herein, phrases such as “from about X to Y” mean “from about X to about Y.” 
     It will be understood that when an element is referred to as being “on”, “attached” to, “connected” to, “coupled” with, “contacting”, etc., another element, it can be directly on, attached to, connected to, coupled with or contacting the other element or intervening elements may also be present. In contrast, when an element is referred to as being, for example, “directly on”, “directly attached” to, “directly connected” to, “directly coupled” with or “directly contacting” another element, there are no intervening elements present. It will also be appreciated by those of skill in the art that references to a structure or feature that is disposed “adjacent” another feature may have portions that overlap or underlie the adjacent feature. 
     Spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper”, “lateral”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the descriptors of relative spatial relationships used herein interpreted accordingly. 
       FIG. 4  shows a cable  51 A with a jacket  57 , in accordance with a first embodiment of the present invention. The jacket  57  includes a plurality of projections  55  extending away from an inner surface  53  of the jacket  57  toward a center of the cable  51 A. In the first embodiment of  FIG. 4 , the plurality of projections  55  is formed by eight projections  55 , which form eight air channels  13  around the inner surface  53  of the jacket  57 . However, as illustrated in other embodiments herein, more or fewer projections  55  may be included, such as six projections, five projections or even three projections. 
     The jacket  57  surrounds a cable core. The cable core may include a first twisted wire pair A, a second twisted wire pair B, a third twisted wire pair C, and a fourth twisted wire pair D. The jacket  57  may be formed of polyvinylchloride (PVC), low smoke zero halogen PVC, polyethylene (PE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE), or other foamed or solid materials common to the cabling art. 
     Each twisted wire pair A, B, C and D includes two insulated conductors. Specifically, the first twisted wire pair A includes a first insulated conductor  69  and a second insulated conductor  71 . The second twisted wire pair B includes a third insulated conductor  73  and a fourth insulated conductor  75 . The third twisted wire pair C includes a fifth insulated conductor  77  and a sixth insulated conductor  79 . The fourth twisted wire pair D includes a seventh insulated conductor  81  and an eighth insulated conductor  83 . 
     Each of the first through eighth insulated conductors  69 ,  71 ,  73 ,  75 ,  77 ,  79 ,  81  and  83  is constructed of an insulation layer surrounding an inner conductor. The outer insulation layer may be formed of a flexible plastic material having flame retardant and smoke suppressing properties, such as a polymer or foamed polymer, common to the cabling art like fluorinated ethylene propylene (FEP), polyethylene (PE) or polypropylene (PP). The inner conductor may be solid or stranded, and may be formed of a conductive metal or alloy, such as copper. In one embodiment, the inner conductor is a solid, copper wire of about twenty three gauge size. 
     As illustrated in  FIGS. 5 ,  7  and  8 , each twisted wire pair A, B, C and D is formed by having its two insulated conductors continuously twisted around each other. For the first twisted wire pair A, the first conductor  69  and the second conductor  71  twist completely about each other, three hundred sixty degrees, at a first interval w along the length of the cable  51 . The first interval w may purposefully vary within a first range of values (randomly or in accordance with an algorithm) along the length of the cable  51 . 
     For the second twisted wire pair B, the third conductor  73  and the fourth conductor  75  twist completely about each other, three hundred sixty degrees, at a second interval x along the length of the cable  51 . The second interval x may purposefully vary within a second range of values (randomly or in accordance with an algorithm) along the length of the cable  51 . 
     For the third twisted wire pair C, the fifth conductor  77  and the sixth conductor  79  twist completely about each other, three hundred sixty degrees, at a third interval y along the length of the cable  51 . The third interval y may purposefully vary within a third range of values (randomly or in accordance with an algorithm) along the length of the cable  51 . 
     For the fourth twisted wire pair D, the seventh conductor  81  and the eighth conductor  83  twist completely about each other, three hundred sixty degrees, at a fourth interval z along the length of the cable  51 . The fourth interval z may purposefully vary within a fourth range of values (randomly or in accordance with an algorithm) along the length of the cable  51 . 
     Each of the twisted wire pairs A, B, C and D has a respective first, second, third and fourth mean value within the respective first, second, third and fourth ranges of values. Each of the first, second, third and fourth mean values of the intervals of twist w, x, y and z may be unique, e.g., different from the other three values. More information about the above-described twist modulation can be found in the Assignee&#39;s U.S. Pat. No. 6,875,928 and published U.S. Application 2008/0073106, which are incorporated herein by reference. 
     As illustrated in  FIGS. 7-9 , the first through fourth twisted wire pairs A, B, C and D may be separated from each other by a star-shaped or plus-shaped separator  85 A (sometimes referred to as a flute, isolator or cross-web), and may be twisted together with the separator  85 A in a direction  89  to form a stranded core. The core strand direction  89  may be opposite to the pair twist directions of the first through fourth twisted wire pairs A, B, C and D, however this is not a necessary feature. 
     In preferred embodiments, the strand length of the core is about five inches or less, more preferably about four inches or less. In a more preferred embodiment, the core strand-length is purposefully varied, or modulates, from an average strand length along a length of the cable  51 . Core strand modulation can assist in the reduction of alien crosstalk. For example, the core strand length could modulate between two inches and four inches along the length of the cable  51 , with an average value of three inches. 
     Other sizes and shapes of separators may be employed in combination with the present invention, such as a generally flat tape separator  85 B (which separates two twisted wire pairs from the other two twisted wire pairs, as depicted in  FIGS. 5-6 ). The separator  85 A or  85 B may be formed of any solid or foamed material common to the cabling art, such as a polyolefin or fluoropolymer, like polyethylene (PE) or fluorinated ethylene propylene (FEP). 
     The cable  51 A of the first embodiment of the invention has eight projections  55  forming eight air channels  13 . The cable  51 A of the first embodiment has no separator  85 A or  85 B. The cable  51 B of the second embodiment of the invention has a jacket  57 A with six projections  55  forming six air channels  13 . The cable  51 B of the second embodiment has a generally flat tape separator  85 B. 
     The cables  51 A and  51 B of the first and second embodiments both include an identical core wrap  30 . The core wrap  30  at least partially surrounds the cable core. In the depicted first and second embodiments, the core wrap  30  is formed by a sheet of material with a length as long as the cable  51 A or  51 B, a width which is slightly larger than a circumference of the cable core (to permit an overlap), such that the core wrap  30  completely surrounds the cable core along a length of the cable  51 A or  51 B. Hence, the core wrap  30  abuts the plurality of projections  55  of the jacket  57  and  57 A. The wires of the twisted wire pairs A, B, C and D are prevented from contacting the plurality of projections  55  and also prevent from entering into an air channel  13 . 
     The core wrap  30  may include an adhesive layer and may partially overlap itself at an overlap area  31 . The overlapped portions of the core wrap  30  may be adhered to each other by the adhesive layer. The adhesive layers may be applied to the entire inner surface of the core wrap  30  facing the center of the cable  51 A or SIB. Alternatively, the adhesive layer may be applied to just a strip of the core wrap  30  adjacent to the edge of the core wrap  30  where the overlap area  31  occurs. In a preferred embodiment, the adhesive layer creates a substantially air tight connection between the overlapped portions of the core wrap  30 . Instead of an adhesive layer, the core wrap  30  may be heated, such that the material forming the core wrap  30  adheres to itself in the overlap area  31 . 
     In a preferred embodiment, the core wrap  30  is formed of a polyester material (like MYLAR) or a similar non-conductive material. In a preferred embodiment, the core wrap  30  has a thickness of about 0.8 mils or less, although other thicknesses are possible. 
       FIG. 7  is a perspective view of a cable  51 C in accordance with a third embodiment of the present invention. The cable  51 C of the third embodiment of the invention has the jacket  57 A with six projections  55  forming six air channels  13 . The cable  51 B of the third embodiment has the plus-shaped separator  85 A. 
     The cable  51 C of the third embodiment includes a core wrap  30 A which only partially surrounds the cable core, leaving an air gap  32  along the length of the cable  51 C. The core wrap  30 A is formed by a tape traveling around the cable core in an open helix shape. In the depicted embodiment, the tape would have a length much greater than a length of the cable  51 C and a width which is about 0.2 inches. The core wrap  30 A is helically wrapped about the cable core at an angle of about thirty degrees, which creates a helical air gap  32  of about 0.4 inches along the length of the cable  51 B. Of course, different tape widths and angles of helical winding may be employed so as to change the dimensions of the air gap  32 . The core wrap  30 A will assist in keeping the cable core tight and keeping wires of the cable core out of the air channels  13 . 
     The core wrap  30 A may optionally include an adhesive layer on its surface facing the cable core to adhere the core wrap  30 A to the insulation layers of the twisted wire pairs A, B, C and D and/or the edges of the separator  85 A or  85 B. Instead of an adhesive layer, the core wrap  30 A may be heated, such that the material forming the core wrap  30 A adheres itself to the insulation layers of the twisted wire pairs A, B, C and D and/or the edges of the separator  85 A or  85 B. In a preferred embodiment, the core wrap  30 A is formed of a polyester material (like MYLAR) or a similar non-conductive material. In a preferred embodiment, the core wrap  30 A has a thickness of about 0.8 mils or less, although other thicknesses are possible. 
       FIG. 8  is a perspective view of a cable  51 D in accordance with a fourth embodiment of the present invention.  FIG. 9  is a cross sectional view taken along line IX-IX in  FIG. 8 . The cable  51 D of the fourth embodiment of the invention has a jacket  57 B with twelve projections  55  forming twelve air channels  13 . The cable  51 D of the fourth embodiment has the plus-shaped separator  85 A. 
     The cable  51 D of the fourth embodiment includes a core wrap  30 B which completely surrounds the cable core along the length of the cable  51 D. The core wrap  30 B is formed by a tape traveling around the cable core in an overlapping helix shape. In the depicted embodiment, the tape would have a length much greater than a length of the cable  51 D and a width which is about 0.2 inches. The core wrap  30 B is helically wrapped about the cable core at an angle of about 5 to 10 degrees, which creates a continuous helically-shaped, small overlapped area  31  with the previous helical wrap. Of course, different tape widths and angles of helical winding may be employed so as to change the extent of the overlapped area  31 . 
     The core wrap  30 B may optionally include an adhesive layer on its surface facing the cable core to adhere the core wrap  30 B to the insulation layers of the twisted wire pairs A, B, C and D and/or the edges of the separator  85 A or  85 B. Alternatively, the adhesive layer may be applied to just a strip of the core wrap  30 B adjacent to the edge of the core wrap  30 B where the overlap area  31  occurs. In a preferred embodiment, the adhesive layer creates a substantially air tight connection between the overlapped portions of the core wrap  30 B. Instead of an adhesive layer, the core wrap  30 B may be heated, such that the material forming the core wrap  30 B adheres to itself in the overlap area  31 . 
     In a preferred embodiment, the core wrap  30 B is formed of a polyester material (like MYLAR) or a similar non-conductive material. In a preferred embodiment, the core wrap  30 B has a thickness of about 0.8 mils or less, although other thicknesses are possible. 
     With the core wraps  30 ,  30 A and  30 B, the air channels  13  may be made very large in width, yet the risk of a wire of a twisted wire pair A, B, C, D entering one of the air channels  13  is greatly diminished. For example, the width of each air channel  13  may be greater than a diameter of a wire of a twisted wire pair of the cable core. More preferably, the width of each air channel  13  may be greater than twice the diameter of a wire of a twisted wire pair of the cable core. 
     Although the cables illustrated in the drawing figures have included four twisted wire pairs, it should be appreciated that the present invention is not limited to cables having only four twisted wire pairs. Cables having other numbers of twisted wire pairs, such as one twisted wire pair, two twisted wire pairs or even twenty-five twisted wire pairs, could benefit from the structures disclosed in the present invention. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.