An electric cable

Abstract: The present invention relates to an electric cable which includes at least one cable part and at least one shield which surrounds at least one cable part, and which further includes a plastic or a rubber sheath which embraces the cable part or parts and the shield, wherein each cable part includes a conductor made of copper wire or some other electrically conductive material, and a plastic or a rubber insulating layer. According to the invention, the shield (4) is comprised of one or more prefabricated, woven or braided bands which are placed longitudinally around the cable part or parts (1). The total width of the shield band or bands (4) is roughly equally as large as the perimeter of the underlying construction.

Description: TECHNICAL FIELD The present invention relates to an electric cable which includes at least one cable part, at least one shield or screen which surrounds said at least one part, and a plastic or a rubber sheath, which surrounds said part or said parts and the shield. Each cable part includes an electrical conductor made of copper wire or other conductive material, and a plastic or a rubber isolating layer. SE-B- 315 643 is considered to be closest prior art and discloses the features mentioned in the preamble of claim 1. BACKGROUND ART Shielded cables are used in environments in which there is a risk of electrical and/or magnetic disturbances occurring. The shield construction, and therewith also the function of the shield, will thus depend on the environment from which the cable shall be protected, i.e. shielded, against. The simplest shielded cable is a so-called coaxial cable which comprises an insulated conductor or cable part which is surrounded by a shield of spirally-wound wires or a braided shield or screen. The shield is embraced by cable sheathing. The effectiveness of the shield can be further enhanced by placing metal foil between said cable part and the shield and/or between the shield and the cable sheathing. When shielding cables by means of spirally-wound wires, it may be difficult to maintain a sufficient tightness or compactness of the shield when bending the cable for instance, since bending of the cable will cause the shield wires to slide apart on the outer surface of the cable bend. The shielding function is thus impaired at these locations, which is naturally a disadvantage. Braided shields are comprised of a large number of wires which are placed in accordance with a given pattern. Such shields are encumbered with many manufacturing drawbacks. One of the main drawbacks resides in difficulties in achieving continuous production, as a result of the necessity to stop production in order to effect requisite wire changes. In addition, braiding is a relatively slow process and is therefore usually carried out in a separate production step. Another drawback resides in connecting the braiding. After having stripped the cable, a sleeve is pressed in beneath the braiding when making a crimp connection of some similar connection. Because of the configuration of the braiding this may be difficult to achieve at times, among other things due to difficulty in inserting the sleeve to the shield. Another drawback with braided shields is that connection of the shield to an electric contact is effected separately. When stripping the cable, the braided shield is loosened from said cable part or parts and then cut and shaped into a separate conductor. This task is both difficult and time-consuming and there is also a risk that the cable part or cable parts will be cut and therewith damaged. SUMMARY OF THE INVENTION The object of the present invention is to provide an alternative method of shielding a cable of the aforesaid kind which leads to improved qualities from a process, shielding and handling aspect. The inventive concept provides a novel shield which has the same electrical properties as a braided shield but which affords further positive effects from a process and handling aspect in particular. This has been achieved with an inventive cable having the characteristic features set forth in the accompanying Claims. According to the invention, the shield is comprised of one or more bands which are woven and which comprises (tinned) copper wires, optionally with transversely extending connecting wires of some other material. The longitudinally extending wires may be comprised of material other than copper. The shielding band or bands is/are laid in the direction of the longitudinal axis of the cable. The invention will now be described in more detail with reference to a preferred exemplifying embodiment thereof and also with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a cable comprising a cable part and a surrounding shield according to prior art, a so-called coaxial cable. Figure 2 illustrates an embodiment of the shield with an invisible overlap. Figures 3a and 3b illustrate a further embodiment of the inventive shield with a locking overlap. Figure 4 is a schematic illustration of the construction of the shielding band. Figure 5 illustrates schematically the shielding band formed to provide an electrical connection. BEST MODE OF CARRYING OUT THE INVENTION Figure 1 is a cross-sectional view of a cable according to prior art having solely one cable part 1 and a shield 4 which embraces said one part, i.e. a so-called coaxial cable. It will be understood that the cable may include several parts, of which each part or only some parts is/are embraced by an inventive shield, and also that the parts of multipart cables can be embraced by respective further shields, as explained in more detail herebelow. Each cable part 1 includes a conductor 2 which may consist of copper wire or some other electrically conductive material, which is optionally tinned, and an insulating layer 3 comprised of a plastic or a rubber material or a mixture of said materials, optionally halogen-free. The cable is provided externally with a protective, holding sheath or jacket 5 which is comprised of an insulating layer of plastic or rubber material, or a mixture of these materials, optionally halogen-free. The shield 4 is comprised of one or more bands which is/are woven. The bands are made of copper wire, which may optionally be tinned, or some other suitable electrically conductive material. The shield band or bands 4 is/are laid longitudinally. It is assumed in the following, however, that only one band is used and that good shielding is the main requirement. The woven band, shown in more detail in Figure 4, is constructed of longitudinally extending wires 6 which are held together by transverse, connecting wires 7, these wires optionally comprising a material different from the longitudinally extending wires 6. Figure 2 illustrates an embodiment of the shield band 4 in which the longitudinally extending threads 6 which "cover" the perimeter of the construction, i.e. the perimeter of the cable part 1 lying beneath the shield, have a diameter which is larger than the overlapping, longitudinally extending wires 6a along the side edges of the shield band 4. The shield band 4 may also be provided with wires whose diameters decrease successively out towards the side edges. The advantage afforded hereby is that the diameter of the cable will be smaller at the overlap and that the cable will be smoother, among other things. Figures 3a and 3b illustrate a combination of longitudinally extending wires of mutually different diameters. Among other things, the combination provides the advantage that the overlap obtains a locking function, because the longitudinally extending wires of larger diameter along one side edge of the band 4 "hook firmly" in the spaces between longitudinally extending wires of smaller diameter along the other side edge of the band 4. The combination also provides the advantage of a smaller cable diameter at the overlap. Figure 5 illustrates a shield band 4 constructed in accordance with the invention and having the important advantage that, as a result of the band construction, an electric connection or electric contact can be readily achieved by twisting the shield band to form a separate conductor after stripping the cable sheath. This is difficult and time-consuming to achieve with a braided shield of conventional construction, because a braided shield must be sliced or cut and then folded to form a conductor. In addition, there is a risk that the cable parts will be damaged when cutting the shield. The shield construction may have a double function in the case of coaxial cables. In this case, the shield band will function as an electric conductor and also as a shield. By electric conductor is meant here that the conductor formed by said cable part and the shield band shall have roughly the same areas, or areas which are sufficiently large to ensure that the conductor function of the shield band will be realized. The shielding ability of the shield band is adapted to the physical tightness of the band. When greater demands are placed on the shielding ability of the shield, or when a more tightly wound or denser shield is desired, the shield construction can be complemented with metal foil. The metal foil is placed between cable part and shield and/or between shield and cable sheath, and may consist of a pure Al-foil, Al-coated plastic foil, a pure Cu-foil, Cu-coated plastic foil or a µ-metal foil. The metal side shall be turned to face the shield band. When the metal foil lies between the cable part and the shield band, the metal foil has the dual function of shielding the cable and of providing a solder guard when connecting solder contacts to the shield. The shield construction is sheathed or banded so as to hold the shield band together. The sheathing consists of an insulating layer of a plastic or a rubber material, or a mixture of these materials, optionally halogen-free. Banding is effected with a plastic band or a metal foil, in accordance with the aforegoing. It will be understood that the invention is not restricted to the aforedescribed and illustrated embodiments, and that modifications can be made within the scope of the following Claims.

Claims: An electric cable including at least one cable part, wherein each cable part includes a conductor which is made of copper wire or some other electrically conductive material, and a plastic or a rubber insulating layer, at least one shield which surrounds at least one cable part, and a plastic or rubber cable sheath which surrounds said cable part or parts and said shield, the shield being comprised of one or more prefabricated bands placed longitudinally around the cable part or cable parts, the total width of the shield band or bands being greater than the perimeter of the underlying construction so as to form an overlap, characterized in that the shield band or bands (4) is/are woven and is/are comprised of longitudinally extending wires (6) and transverse holding wires (7), and in that the overlapping wires (6a) which extend longitudinally along the side edges of the band have a smaller diameter than the remaining wires (6). An electric cable including at least one cable part, wherein each cable part includes a conductor which is made of copper wire or some other electrically conductive material, and a plastic or a rubber insulating layer, at least one shield which surrounds at least one cable part, and a plastic or rubber cable sheath which surrounds said cable part or parts and said shield, the shield being comprised of one or more prefabricated bands placed longitudinally around the cable part or cable parts, the total width of the shield band or bands being greater than the perimeter of the underlying construction so as to form an overlap, characterized in that the shield band or bands (4) is/are woven and is/are comprised of longitudinally extending wires (6) and transverse holding wires (7), and in that the longitudinally extending wires (6) have mutually different diameters, so as to obtain a locking effect at the overlap (8). An electric cable according to Claim 1 or 2, characterized in that the shield band (4) is manufactured from copper wires or some other electrically conductive material. An electric cable according to Claim 1 or 2, characterized in that the total cross-sectional area of the shield band or bands (4) is of the same magnitude as the conductive area of the cable part (1). An electric cable according to Claim 1 or 2, characterized in that metal foil is placed between the shield band or bands (4) and the cable part (1) or cable parts. An electric cable according to Claim 1 or 2, characterized in that metal foil is placed between the cable sheathing (5) and the shield band or bands (4). An electric cable according to Claim 5 or 6, characterized in that the metal foil consists of aluminium, copper, plastic-coated aluminium or copper, or µ-metal. An electric cable according to Claim 7, characterized in that the metal side of the plastic-coated material faces towards the shield band (4). An electric cable according to Claim 1 or 2, characterized in that the cable includes several parts (1), and in that one or more shield bands (4) are placed around each cable part or pairs of cable parts. An electric cable according to Claim 1 or 2, characterized in that the cable includes several parts (1), and in that one or more shield bands (4) are placed solely around given cable parts. An electric cable according to Claim 9 or 10, characterized in that a further shield band (9) or further shield bands is/are placed externally around the shielded and unshielded cable parts (1), inwardly of the cable sheathing (5). An electric cable according to Claim 11, characterized in that the further shield band or bands (9) is/are constructed in the same fashion as the shield band (4) extending around the cable part or parts (1). An electric cable according to Claim 12, characterized in that metal foil is placed between the further shield band (9) and the underlying construction, or between the cable sheathing (5) and the further shield band (9).

Inventors: BORTAS MATS OLA, EFRAIMSSON LARS OLOF, NYBERG AGNE HUGO, BORTAS, MATS OLA, EFRAIMSSON, LARS OLOF GUNNAR, NYBERG, AGNE HUGO
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1993
Main classification: H01B11
IPC codes: H01B11, H01B7, H01B9