AN AERIAL LINE TENSIONING DEVICE

Abstract: An aerial line tensioning device which uses an outer casing to protect the slide mechanism and the oscillation mechanism of the gas spring type aerial line tensioning device from disturbance, the slide mechanism comprising a cylinder case and a cylinder rod, and the oscillation mechanism being used to oscillate a connecting bar for connecting the cylinder and the aerial line. This construction improves operation reliability of the tensioning device and reduces maintenance service requirements.

Description: The present invention relates to an overhead wire tensioning device according to the preamble of claim 1. Such a tensioning device is known from JP-A-35-21205 and can be used for such applications as maintaining a tension of overhead wire for railways. Overhead wire, in particular overhead wire for railways (such as main wire, support wire and trolley lines), is required to be tensioned appropriately at all times because the tension of the overhead wire is affected by such factors as the elongation and shrinking due to temperature changes, elongation due to creeping and wear of the material of the wire, and the tilting of the supporting structures over time. It is particularly desirable to be able to automatically adjust the tension of the overhead wire, and eliminate the need for maintenance work. Conventionally known automatic tensioning devices for maintaining the tension of overhead wire at a constant level include those using pulleys to produce a tension from the gravitational force acting on a weight, and those using springs to produce a tension from the spring force of a spring. The pulley type can provide a favorable performance in maintaining the tension at a constant level, but the work involved in installation is significant and a regular maintenance work is required to prevent degradation of the wire. Tensioning devices using gas springs (such as those disclosed in Japanese patent laid open publication No. 6-16068) have drawn attention in this regard as they allow the entire assembly to be highly compact and light-weight, and eliminate the need for constant maintenance work. A gas spring type tensioning device of this type includes a cylinder case defining a gas chamber and having one end of the device attached to one of a fixed end and the overhead wire, and a cylinder rod extending out of the cylinder case and having an end attached to the other of the fixed end and the overhead wire. As the cylinder rod and the cylinder case is required to be axially slidable relative to each other, if the mechanism for permitting this relative sliding movement fails to operate properly, the sliding resistance between them could increase to such an extent that a desired tension may not be achieved. Therefore, it has been desired to improve the device so as to eliminate such a possibility. A gas spring type tensioning device of this type additionally includes a tension rod extending between the cylinder and the overhead-wire and having an end pivotally attached to the cylinder via a trunnion shaft to accommodate the swaying movement of the overhead wire. If such a pivotable arrangement fails, this tension rod mechanism becomes unable to accommodate the swaying movement of the overhead wire, and this likewise may prevent maintenance of a desired tension. The above-mentioned tensioning device known from JP-A-35-21205 is also unable to accomodate the swaying movement of an overhead wire. In view of such problems of the prior art, a primary object of the present invention is to provide an overhead wire tensioning device which can favorably maintain a tension of overhead wire at a constant level, and is highly reliable in use without requiring any constant maintenance work. Such object is achieved by the present invention with an overhead wire tensioning device according to the preamble of claim 1 comprising the features included in the characterizing portion of claim 1. Further embodiments of the present invention are included in the dependent claims. Preferred embodiments the present invention are described in the following with reference to the appended drawings wherein Figure 1 is a sectional view of a tensioning device embodying the present invention; Figure 2 is a sectional view taken along line II-II of Figure 1; Figure 3 is a plan view as seen from a right end of Figure 2; Figure 4 is a sectional view of an alternate embodiment of the tensioning device according to the present invention; Figure 5 is a sectional view of another alternate embodiment of the tensioning device according to the present invention; Figure 6 is a sectional view taken along line VI-VI of Figure 5; and Figure 7 is a plan view as seen from a right end of Figure 6. Figure 1 is a sectional view of a tensioning device embodying the present invention, Figure 2 is a sectional view taken along line II-II of Figure 1, and Figure 3 is a plan view as seen from a right end of Figure 2. This tensioning device 1 comprises an outer casing 2 having a cylindrical shape with a closed bottom end, a hollow cylinder case 3 received in the outer casing 2, and a cylinder rod 6 having an end fixedly attached to a bottom portion 4 of the outer casing 1 on the right end thereof, and another end passed into the cylinder case 3 via a through hole 3a. A cylinder flange 7 is attached to the other end of the cylinder case 3 with threaded bolts or the like. As shown in Figure 2, a gas chamber 3b is defined in the cylinder case 3, and is filled with high pressure nitrogen gas. A liquid chamber 8a filled with liquid is defined inside the gas chamber 3b by a bellows 8 which is fixedly attached to the right end of the cylinder case 3 at an end thereof, and capable of expanding and shrinking in the axial direction. The other end of the cylinder rod 6 is passed into this liquid chamber 8a. As shown in Figures 1 and 3, slots 4a and 4b are formed in the bottom portion 4 of the outer casing 2 on the right end thereof. Trunnion shafts 10 and 11 are formed on either side of the cylinder case 3 at a right end portion thereof to pivotally support one ends of a pair of tension bars 12 and 13 serving as connecting rods. These tension bars 12 and 13 extend out of the outer casing 2 through the slots 4a and 4b in the right bottom portion thereof, and the other ends are connected to each other by a connecting plate 14. An overhead wire bracket 15 is provided in a central part of the connecting plate 14. This arrangement accommodates the difference in the extending direction of the overhead wire which is connected to the bracket 15 but not shown in the drawing. Furthermore, any swaying movement of the overhead wire can be accommodated by the pivoting movement of the tension bars 12 and 13 around the trunnion shafts 10 and 11 to the extent permitted by the slots 4a and 4b. The trunnion shafts 10 and 11 are located inside the outer casing 2, and are somewhat spaced away from the inner wall of the outer casing 2. Therefore, even when the outer casing 2 is dented or otherwise deformed by external influences, the pivoting movement of the tension bars 12 and 13 would not be interfered by it. As shown in Figure 2, a pair of guide rods 16 and 17 extend between the right bottom end portion 4 of the outer casing 2 and the left bottom end portion 5 of the outer casing 2. A guide mechanism for the cylinder case 3 is formed by passing the guide rods 16 and 17 through guide holes 7a and 7b formed in the cylinder flange 7. The left bottom end portion 5 of the outer casing 2 is firmly prevented from coming off from the outer casing 2, and is centrally provided with a pole bracket 18 for the support structure. The guide mechanism comprising these guide rods 16 and 17 and the cylinder flange 7 is somewhat separated from the inner wall of the outer casing 2. Therefore, even when the outer casing 2 is dented or otherwise deformed by external influences, the guide mechanism can maintain its function. In the gas spring tensioning device 1 described above, the pressure of the high pressure gas in the gas chamber 3b is applied to the liquid chamber 8a via an end surface (a bellows cap or a pressure receiving surface) of the bellows 8 to actuate the bellows 8 in the direction to shrink. As this force acts in the direction to push the cylinder rod 6 out of the cylinder case, the two brackets 15 and 18 are urged toward each other. The tension of the overhead wire acting upon the bracket 15 is transmitted to the cylinder case 3 via the tension bars 12 and 13 and the trunnion shafts 10 and 11 so as to pull the cylinder rod 6 into the cylinder case 3. Therefore, the relative position of the cylinder rod 6 is determined by the balance between the tension of the overhead wire and the gas pressure in the gas chamber 3b. When changes in the surrounding temperature causes the overhead wire to elongate and shrink, they also affect the gas in the gas chamber 3b. For instance, when a rise in the surrounding temperature elongates the overhead wire, the gas in the gas chamber 3b expands and this in turn causes to apply a tension to the overhead wire so as to cancel the elongation of the overhead wire. To maintain the tension of the overhead wire without regard to the surrounding temperature, the volume of the gas should be determined as given in the following. V=ALαT where A: pressure receiving area of the cylinder rod L: length of the overhead wire α: line expansion coefficient of the overhead wire T: absolute temperature. When the expansion of the oil in the liquid chamber is taken into consideration, the optimum volume of the gas will be given by the following equation. V = (ALα - V oil β)T where V oil : volume of the oil β: volume expansion coefficient of the oil By thus determining the pressure of the gas in the gas chamber 3b and the volume of the chamber 3b so as to match the elongation and shrinkage of the overhead wire due to the changes in the surrounding temperature with the retraction and extension of the cylinder rod 6 due to the expansion of the gas chamber 8a, it is possible to automatically keep the tension of the overhead wire at a constant level without regard to the change in the surrounding temperature. Figure 4 shows an alternate embodiment of the present invention in which a bracket 20 is attached to a side of the outer casing 2 so that the tensioning device 1 may be suspended from a pole P by using a suspension rod 21, and the direction of the movement of the cylinder case 2 may coincide with the extending direction of the overhead wire. The structure of this tensioning device 1 is otherwise similar to that of the preceding embodiment. Figure 5 is a sectional view of another embodiment of the tensioning device according to the present invention, Figure 6 is a sectional view taken along line VI-VI of Figure 5, and Figure 7 is a plan view as seen from a right end of Figure 6. This tensioning device 31 comprises an outer casing 32 having a cylindrical shape with a closed bottom end, a hollow cylinder case 33 received in the outer casing 32 and having an end fixedly attached to a bottom portion 34 of the outer casing 31 on the right end thereof (on the side of the overhead wire), and a cylinder rod 36 having a base end passed into the cylinder case 33 via a through hole 33a. The other end of the cylinder case 33 is supported by the outer casing 31 via a support member 37. As shown in Figure 6, a gas chamber 33b is defined in the cylinder case 33, and is filled with high pressure nitrogen gas. A liquid chamber 38a filled with liquid is defined inside the gas chamber 33b by a bellows 38 which is fixedly attached to the left end of the cylinder case 33 at an end thereof, and capable of expanding and shrinking in the axial direction. The other end of the cylinder rod 36 is passed into this liquid chamber 38a. As shown in Figures 5 and 7, slots 34a and 34b are formed in the bottom portion 34 of the outer casing 32 on the right end thereof. Trunnion shafts 40 and 41 are formed on either side of the cylinder case 33 at a left end portion thereof to pivotally support one ends of a pair of tension bars 42 and 43 serving as connecting rods. These tension bars 42 and 43 extend out of the outer casing 32 through the slots 34a and 34b in the right bottom portion thereof, and the other ends are connected to each other by a connecting plate 44. An overhead wire bracket 45 is provided in a central part of the connecting plate 44. This arrangement accommodates the difference in the extending direction of the overhead wire which is connected to the bracket 45 but not shown in the drawing. Furthermore, any swaying movement of the overhead wire can be accommodated by the pivoting movement of the tension bars 42 and 43 around the trunnion shafts 40 and 41 to the extent permitted by the slots 34a and 34b. As shown in Figure 6, the left bottom end portion 35 of the outer casing 32 is firmly prevented from coming off from the outer casing 32, and is centrally provided with a pole bracket 48 for the support structure. The cylinder case 33, in particular the sliding mechanism for the cylinder rod 36, is somewhat separated from the inner wall of the outer casing 32. Therefore, even when the outer casing 32 is dented or otherwise deformed by external influences, the cylinder rod 36 can continue to function properly. The structure and operation of this embodiment are otherwise similar to those of the preceding embodiments, and are therefore not described again. A gas spring arrangement was used in the above described embodiments, but, as can be readily appreciated, may consist of other spring mechanisms such as coil springs.

Claims: A tensioning device for applying a prescribed tension to an overhead wire, comprising: a tubular outer casing (2; 32) having one end connected to a fixed part; a spring mechanism received in the tubular outer casing (2; 32) and having a first end fixed inside the outer casing (2; 32); and a connecting rod (12, 13; 42, 43) having a first end connected to the overhead wire, and another end received inside said outer casing (2; 32) and supported by the other end of the spring mechanism, said first end of the connecting rod (12, 13; 42, 43) extending out of a slot (4a, 4b; 34a, 34b) which is formed at an opposite end of the outer casing (2; 32), characterized in that the spring mechanism comprises a gas spring including a cylinder case (3; 33) defining a sealed gas chamber (3b; 33b) filled with high pressure gas, whereby an oil chamber (8a, 38a) capable of expanding and shrinking so as to transmit pressure is provided in said gas chamber and, in a first alternative a cylinder rod (6) having a first end passed into the oil chamber (8a) is provided while the other end of the cylinder rod (6) is fixedly whereby the oil chamber (8a) together with the cylinder case 3 secured inside the outer casing (2; 32); whereby the oil chamber (8a) together with the cylinder case 3 is movable in an axial direction inside the outer casing (2) and whereby the other end of the connecting rod (12, 13) is pivotally supported by the cylinder case (3) so as to accommodate a swaying movement of the overhead wire, or, in a second alternative, whereby the cylinder case (33) is fixedly secured inside the outer casing (32) and the cylinder rod (36) is movalle in an axial direction inside the cylinder case (33), and whereby the other end of the connecting rod (42, 43) is pivotally supported by the other end of the cylinder rod (36) and that the slot (4a, 4b; 34a, 34b) is elongated in a direction of the swaying movement of the overhead wire, so that a swaying movement of the overhead wire is accommodated by a pivoting movement of the connecting rod (12, 13; 42, 43) to an extent permitted by the slot (4a, 4b; 34a, 34b). The overhead wire tensioning device according to claim 1, wherein a gap is defined between an inner wall of the outer casing (2; 32) and at least one of the cylinder case (3; 33) and the cylinder rod (6; 36).

Inventors: AGEISHI SATOSHI, AMANO HIROSHI, KONTA SHOJI, NARUMIYA YOSHIO, SHINBORI TAKEYOSHI, UCHIDA TAKESHI, UCHIKOSHI TORU, WAKABAYASHI YOSHINORI, AGEISHI, SATOSHI, AMANO, HIROSHI, KONTA, SHOJI, NARUMIYA, YOSHIO, SHINBORI, TAKEYOSHI, UCHIDA, TAKESHI, UCHIKOSHI, TORU, WAKABAYASHI, YOSHINORI
Applicants: DENGYO INC, NHK SPRING CO LTD, TOKAI RYOKAKU TETSUDO KK, CENTRAL JAPAN RAILWAY COMPANY, DENGYO INCORPORATED, NHK SPRING CO.LTD.
Application year: 1997
Main classification: B60M1
IPC codes: B60M1