The invention generally relates to electrical signal transmission cables, and more particularly relates to a signal transmission cable assembly having an ungrounded sheath that contains electrically conductive particles surrounding the signal conductors.
The need for higher speed in vehicle data connectivity is increasing. This rapid growth is a result of the demand to have collision avoidance systems, lane departure warning systems, automatic braking systems, adaptive cruise control systems, and pedestrian detection systems incorporated into vehicles to support advanced driver assistance systems (ADAS). ADAS is the first step towards the larger goal of autonomous driving systems.
ADAS relies on many high resolution sensors that convey information to a central control module which compiles the data and decides how to best react to the situation. Due to the large amount of information (data) to be transferred from each high resolution sensor to the control module, data connectivity within the vehicle must be able to transfer the data quickly and reliably. The data connectivity must also be secure, in order to protect the information within the vehicle from outside attack and disruptions by individuals intent on causing malfunctions and damage to the vehicle.
As the ADAS systems within the vehicle become more complex and take responsibility for more control of the vehicle, higher data rates and bandwidth will be required driving the need for more complex data transmission lines.
The most popular form of data transmission line used for in-vehicle data connectivity today and the foreseeable future are cable pairs using differential signaling methods. Unshielded twisted pair (UTP) cables are the most commonly used differential pair cables due to their cost advantage and ability to reliably deliver data between two or more electronic devices. UTP cables are acceptable for lower data rate technologies in the 10 to 20 megabits per second (Mbps) range having a bandwidth in the 5 to 30 megahertz (MHz) range.
Twisted pair (TP) data cables have the unique feature that each line in the pair is intimately interacting electromagnetically with the other line of the pair. This electromagnetic (EM) interaction is not contained to just between the two lines 12,14 in the TP cable, but is about them in a cloud like form E as illustrated in
As data rates increase, the containment of the EM cloud becomes even more important. At higher data rates, the use of an insulative jacket 18 surrounding the twisted pair 12, 14 as shown in
As illustrated in
For data rates above 100 Mbps having a bandwidth greater than 150 MHz, a metal shield is used about the twisted pair and is known as shielded twisted pair (STP) cable. The STP cable is common in industry but requires that both ends of the shield are connected to an electrical ground. STP cable also requires the use of a shielded connector as the metal shield must contain every section of the TP cable. Since the shield is made of a continuous metal section, both ends must be properly grounded. If the metal shield is not properly grounded, the shield will act as an antenna potentially re-radiating the signals within shield or picking up EMI and coupling the interference to the conductors within the shield. The addition of the shield to the cable and the addition of metal sections to connected componentry drives additional cost and complexity to the finished system.
Ethernet data transmission protocol is being adopted for data transmission in automotive applications. Early automotive systems adopting Ethernet protocol are running at a data rate of 100 Mbps and require data connectivity that supports a bandwidth of at least 100 MHz. As the systems within the vehicle become more complex and take over more control of the vehicle, higher data rates and bandwidth of the connectivity will be required. Investigation into data protocols transmitting at 1000 Mbps having a bandwidth greater than 700 MHz is underway. However, issues are arising regarding the ability to transfer data at this rate and bandwidth in a cost effective way. Complexity of the vehicle harness routing, bundling of cable, external electromagnetic interference (EMI), and signal integrity (SI) are further complicating efforts to produce data signal cables in a cost effective manner.
Parallel wire transmission lines can also be used for data transmission at these rates. Parallel wire transmission lines are often used to reduce manufacturing burden by eliminating the twisting process, but they may not provide enough protection from electromagnetic interference (EMI) and typically require shielding.
Therefore, a cost effective, automotive data signal cable that is capable of transferring data at rates above 100 Mbps having a bandwidth of at least 100 MHz remains desired. The cable must maintain the ability to protect against EMI, and be able to be bundled and routed within a cable harness without affecting signal integrity.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
According to a first embodiment, a data transmission cable assembly is provided. The data transmission cable assembly includes an elongate first conductor, an elongate second conductor, and a sheath that at least partially axially surrounds the first and second conductors. The sheath comprises a plurality of electrically conductive particles that are interspersed within a matrix formed of an electrically insulative polymeric material.
The plurality of conductive particles may be formed of a metallic material. The plurality of conductive particles may be in the form of filaments, e.g. metallic filaments and/or metallically plated fiber filaments, and/or carbon nanotube filaments. The filaments in the sheath are substantially aligned with one another. The filaments form a plurality of electrically interconnected networks, wherein each network is electrically isolated from every other network. Each network contains less than 125 filaments and/or has a length of less than 13 millimeters. The plurality of conductive particles may alternatively or additionally be formed of masses of an inherently conductive polymeric material. The bulk conductivity of the sheath is substantially equal to the conductivity of the electrically insulative polymeric material.
The sheath may be formed over the first and second conductors via an extrusion process or may be in the form of a film wrapped about the first and second conductors. The first and second conductors may twisted one about the other or may be substantially parallel to one another. The data transmission cable assembly may include a plurality of first conductors and a plurality of second conductors. The data transmission cable assembly does not include a terminal configured to connect the sheath to an electrical ground.
The data transmission cable assembly may further include a metallic shield that at least partially axially surrounds the first and second conductors. The sheath axially surrounds this metallic shield. The data transmission cable assembly does not include a terminal that is configured to connect the metallic shield to an electrical ground.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.
The present invention will now be described, by way of example with reference to the accompanying drawings, in which:
In these figures, reference numbers having the same last two digits are used to designate identical or similar elements.
The inventors have discovered a solution to the problem of the EM cloud extending beyond the exterior of a data cable is an insulative jacket or sheath surrounding the conductors of a twisted pair that includes metallic particles to reduce the EM cloud from the conductors extending beyond the sheath, thereby reducing interaction between the conductors and the surrounding environment. The inventors have observed that the impedance of such a data cable is more consistent along its length and is less subject to variation due to conductive objects near the cable. The sheath does not require a connection to an electrical ground to obtain these benefits.
The cable assembly 110 further includes a sheath 118 that surrounds the twisted pair 116 along the longitudinal axis L of the cable assembly 110, except for the portion that is removed to terminate the conductors 112A, 114A. As illustrated in
As illustrated in
Extruding a polymeric material containing particles produces a skin layer on the outer surface of the extrusion that has a much lower concentration of the particles than the internal portion of the extrusion. Since this skin layer is rich in the dielectric polymeric material 120, the sheath 118 may also provide an electrical insulator for the cable assembly 110.
Without subscribing to any particular theory of operation, the conductive particles 122 in the sheath 118 increase the dielectric constant value of the sheath so that it is higher than the dielectric constant of the base dielectric material 120 causing the sheath 118 to absorb and reflect the EM cloud E from the twisted pair 116 so that the EM cloud E is substantially continued within the sheath 118 as illustrated in
The sheath 118 does not provide all of the advantages of a full metal shield regarding EMI, but the sheath 118 has demonstrated that adequate shielding effectiveness for use in cable assemblies 110 for differential signaling. The electromagnetic behavior of several types of differential signaling protocols (e.g. USB 2.0, Ethernet protocol) were examined and a the cable assembly 110 was shown to contain the necessary EM cloud E and prevent interference and/or interception by known EMI threats. Based on the required extent of shielding needed to be provided by the sheath 118, the conductive particle content in the polymeric material 120 of the sheath 118 can be adjusted to produce the most cost effective solution.
Differential pairs may be designed for use in a J-UTP cable 10 (as shown in
Considerations regarding characteristic impedance must also be taken into account when configuring the composition of the sheath 118. By knowing the exact composition of the conductive particles 122 and polymeric material 120 in the sheath 118, the characteristics of the sheath 118 and the transmission line within the sheath 118 can be optimized for a desired characteristic impedance.
Design parameters of twisted pairs used for differential signaling are well known to those skilled in the art and are based on the materials and geometries applied. When designing the sheath 118, the unique properties of the polymer/metallic composite material must be taken into account and applied to these standard equations.
Comparative tests of the cable assembly 110 versus a standard J-UTP cable 10 were performed and the testing procedures and results are discussed below.
Two identical lengths of cable were prepared, the first a length of J-UTP cable having a characteristic impendence of about 100Ω and the second a length of the cable assembly 110 having a characteristic impedance of about 60Ω. The impedance along the cable was then measured using a time domain reflectometer.
Due to the loading of the EM cloud by the metallic particles in the sheath 118, the cable assembly 110 may have greater signal loss per length than other twisted pair cable types, e.g. J-UTP cables 10. However, since most automotive applications have a cable length of 7 meters or less, the cable assembly 110 can still provide reliable data communication because the signal loss will not be significant over those distances.
In order to reduce losses in the cable, an alternative embodiment of the cable assembly 310 shown in
While the illustrated examples presented herein show a cable assembly having a single twisted pair, alternative embodiments of the invention may be envisioned that have multiple twisted pairs.
Another alternative embodiment of cable assembly 410 is shown in
Accordingly, a data transmission cable assembly is presented. The cable assembly 110 provides an alternate method of containing the EM cloud E about the signal wires 112, 114 and does not require a traditional, continuous metal shield. The sheath 118 of the cable assembly 110 does not require a connection to an electrical ground, simplifying the termination of the cable assembly 110 and thus reducing manufacturing costs. The EM energy flow E is controlled through the differential pair by the conductive particles 122 contained in the sheath 118. This sheath 118 has been shown to provide shielding effects and enables an increase in system bandwidth as compared to a J-UTP cable 10 by:
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.
Number | Name | Date | Kind |
---|---|---|---|
6506492 | Foulger | Jan 2003 | B1 |
20050029000 | Aisenbrey | Feb 2005 | A1 |
20100212952 | Abdelmoula | Aug 2010 | A1 |
20150096782 | Feldmeier | Apr 2015 | A1 |
20160379735 | Koeppendoerfer | Dec 2016 | A1 |