Connecting structure and connecting method for electric cables

Abstract

There is provided a connecting structure for electric cables. A first electric cable includes a first core and a first cover covering the first core. A portion of the first core is exposed from an end of the first cover. A second electric cable includes a second core made of a different metal from that of the first core and a second cover covering the second core. A portion of the second core is exposed from an end of the second cover. A tube is shrunk in a state where the tube accommodates thereinside the portion of the first core and the portion of the second core which are connected to each other. An inside of the tube except for the portion of the first core and the portion of the second core is filled with cured hot-melt.

Claims

1. A connecting structure for electric cables, comprising: a first electric cable including a first core made of a plurality of wires and a first cover covering the first core, wherein a portion of the first core is exposed from an end of the first cover; a second electric cable including a second core made of a plurality of wires and made of a different metal from that of the first core and a second cover covering the second core, wherein a portion of the second core is exposed from an end of the second cover; and a tube which is shrunk in a state where the tube accommodates thereinside the portion of the first core and a portion of the second core which are connected to each other, wherein an inside of the tube being filled with cured hot-melt, the cured hot-melt being located at least between the plurality of wires in the first and second core and between the first and second cover and the first and second core respectively, wherein a hot-melt has a predetermined thickness before being heated such that the cured hot-melt permeates to the gaps between the wires of the first core, between the wires and the first cover, between the wires of the second core, and between the wires and the second cover without excess or insufficient hot-melt, wherein the hot-melt does not permeate a connection portion between the first core and the second core such that the first core and the second core remain electrically connected after the hot-melt has cured wherein the tube comprises an amount of the hot melt therein such that, prior to being shrunk in the state, the thickness of the hot-melt from the inside of the tube to an inside of the hot-melt is greater than a thickness of the tube.

2. A connecting method for electric cables, comprising: connecting a portion of a first core made of a plurality of wires which is exposed from an end of a first cover and a portion of a second core made of a plurality of wires and which is made of a different metal from that of the first core and exposed from an end of a second cover; accommodating the portion of the first core and the portion of the second core together with molten hot-melt inside a tube; and shrinking the tube, wherein an inside of the tube being filled with cured hot-melt, the cured hot-melt being located at least between the plurality of wires in the first and second core and between the first and second cover and the first and second core respectively, wherein a hot-melt has a predetermined thickness before being heated such that the cured hot-melt permeates to the gaps between the wires of the first core, between the wires and the first cover, between the wires of the second core, and between the wires and the second cover without excess or insufficient hot-melt, wherein the hot-melt does not permeate a connection portion between the first core and the second core such that the first core and the second core remain electrically connected after the hot-melt has cured, and wherein the tube comprises an amount of the hot melt therein such that, prior to being shrunk in the state, the thickness of the cured hot-melt from the inside of the tube to an inside of the hot-melt is greater than a thickness of the tube.

3. The connecting method according to claim 2, wherein the accommodating includes: applying the molten hot-melt on an inner surface of the tube; and accommodating the portion of the first core and the portion of the second core inside the tube with the inner surface thereof being applied with the molten hot-melt.

4. The connecting method according to claim 2, wherein the accommodating includes: applying the molten hot-melt on the portion of the first core and the portion of the second core; and accommodating the portion of the first core and the portion of the second core, on which the molten hot-melt is applied, inside the tube.

5. The connecting method according to claim 2, wherein the tube has two distal ends and a middle portion, wherein the middle portion has smaller diameter than a diameter at each distal end.

6. The connecting method according to claim 2, wherein the tube comprises the amount of the hot melt therein such that, prior to being shrunk in the state, the thickness of the hot-melt from the inside of the tube to the inside of the hot-melt is greater than double thickness of the tube.

7. The connecting method according to claim 2, wherein the thickness of the cured hot-melt is evenly applied along a length of the inside of the tube from one axial end of the tube to an opposite axial end of the tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIG. 1 is a front view conceptually illustrating a connecting structure for electric cables according to the present invention;

(3) FIG. 2 is a front view illustrating the connecting structure for electric cables shown in FIG. 1, where the connecting structure is partially cut away;

(4) FIG. 3 is a longitudinal cross-sectional view illustrating the tube used for connecting the electric cables in FIG. 1;

(5) FIGS. 4A to 4F are process diagrams illustrating a sequence of assembling the connecting structure for electric cables shown in FIG. 1, where FIG. 4A to FIG. 4F illustrate each process;

(6) FIG. 5 is a cross-sectional view taken along a line V-V of the electric cable illustrated in FIG. 4F;

(7) FIGS. 6A to 6F are another process diagrams illustrating a sequence of assembling the connecting structure for electric cables shown in FIG. 1, where FIG. 6A to FIG. 6F illustrate each process; and

(8) FIG. 7 is a perspective view illustrating a connecting structure for electric cables according to the related art.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) Hereinafter, a connecting structure for electric cables according to an embodiment of the present invention will be described with reference to FIG. 1 to FIG. 6F.

(10) As shown in FIG. 1, the connecting structure for electric cables according to this embodiment is a connecting structure for electric cables W, which is connected to, for example, an electronic control circuit. This structure directly connects a terminal to a copper electric cable, which is made of the same material as the terminal, by interposing the copper electric cable between the terminal made of copper or copper alloy and an aluminum electric cable. This makes it possible to avoid contact corrosion from occurring at a region (connection portion) where the terminal and the copper electric cable are connected to each other. Therefore, at the connection portion between the terminal and the aluminum electric cable, the occurrence of contact corrosion due to the presence of moisture as in the related art can be avoided. In addition, subsequent electrical and mechanical problems (e.g. an increase in electrical resistance or a decrease in the strength of connection due to the creation of rust) can also be avoided.

(11) In order to obtain such effects, in this embodiment, gaps between wires of each core and between the wires and an insulating sheath (cover) adjacent to the connection portion between the copper electric cable and the aluminum electric cable are made waterproof using hot-melt, thereby making it possible to avoid contact corrosion in the connection portion between the copper electric cable and the aluminum electric cable, and control movement of moisture from the aluminum electric cable side to the copper electric cable side and further to the terminal. Hereinafter, the connecting structure for electric cables according to this embodiment will be described in detail.

(12) Referring to FIG. 1 and FIG. 2, the connecting structure for electric cables 11 is constructed by assembling a first electric cable (hereinafter, referred to as a copper electric cable) 12, a second electric cable (hereinafter, referred to as an aluminum electric cable) 13, a tube (hereinafter, referred to as a heat-shrink tube) 14, and a terminal 15. Among them, the copper electric cable 12, i.e. the first electric cable, is constructed by covering a first core 16 made of a plurality of wires, which are twisted or braided together, with an insulating sheath (hereinafter, referred to as a first outer cover) 17, and extends a predetermined length so as to be connectable between the terminal 15 and the aluminum electric cable 13. In the copper electric cable 12, both ends of the first core 16 are exposed from the first cover 17 by stripping both ends of the first cover 17 to a predetermined length. In this copper electric cable 12, each gap between the wires of the first core 16 or between the wires and the first cover 17 is a gap through which water or gas can flow.

(13) The aluminum electric cable 13, i.e. the second electric cable, is constructed by covering a second core 18, which is made by twisting or braiding a plurality of wires together, with an insulating cover (hereinafter, referred to as a second cover) 19 made of vinyl chloride or the like. In the aluminum electric cable 13, one end of the second core 18 is exposed by a predetermined length from the second cover 19 by stripping one end of the second cover 19 to a predetermined length. In this aluminum electric cable 13, each gap between the wires of the second core 18 or between the wires and the second cover 19, i.e. the insulating cover, is a gap through which water or gas can flow.

(14) The first core 16 is made of copper or copper alloy, and the second core 18 is made of aluminum or aluminum alloy. The cores 16 and 18 are connected to each other by press-contact. This press-contact connection is realized by, for example, directing a welding horn toward a region where respective ends of the cores 16 and 18 are tied together on an anvil (not shown), followed by high-frequency oscillation, so that frictional heat is generated between the cores 16 and 18. In addition, in a cold welding connecting method, connecting is carried out by fitting corresponding ends of the cores 16 and 18 into holes of dice so as to butt to each other, and then pressing the butted section sliding the dice.

(15) In addition, the terminal 15 is realized by punching (pressing) a plate made of copper or copper alloy, followed by bending the plate. A connection portion 20, which has the shape of an angled box or a cylinder, is provided on the leading end side, which is connected to a counterpart terminal, and a press-contact section 21, which connects the first core 16 by press-contact, extends from the base end of the connection portion 20. The press-contact section 21 includes a pair of electric cable barrels 22, which connects one end of the first core 16 by press-contact, and a pair of outer cover barrel 23, which press-contact the first outer cover 17. The press-contact section 21 is connected to the terminal of the copper electric cable 12 by crimping the first core 16 and the first outer cover 17. The shape of the terminal 15 is not specifically limited, and may be of any one of a female terminal and a male terminal.

(16) The connection between the terminal 15 and the copper electric cable 12 is enabled by crimping, which is typically performed. Instead of an aluminum electric cable as an electric cable that is connected to the terminal 15, the copper electric cable 12, which has proved connection reliability due to massive performance evaluation and the result of use. Thus, high-reliability connection is possible based on the result that has been accumulated to dates. In addition, since additional massive performance evaluation, test, or the like is not necessary, it is possible to reduce the cost of development and is advantageous in terms of cost.

(17) In order to accommodate (cover) a portion of the first core 16 (a portion that is exposed from the first cover 17) and a portion of the second core 18 (a portion that is exposed from the second cover 19), which are connected as described above, the heat-shrink tube 14 is disposed around the first cover 17 of the copper electric cable 12 and the second cover 19 of the aluminum electric cable 13, with hot-melt 24 being interposed therebetween. The heat-shrink tube 14 is a tube that self-shrinks when heat is applied thereto. As shown in FIG. 3, hot-melt 24 having a predetermined thickness is applied in advance. Thus, it is possible to shrink the heat-shrink tube 14 while melting the hot-melt 24 by applying heat to the heat-shrink tube 14, which is fitted in advance around any one of the copper electric cable 12 and the aluminum electric cable 13, from the outside.

(18) In this case, due to the shrinking force of the heat-shrink tube 14, it is possible to make the molten hot-melt 24 permeate between a portion of the first core 16 and a portion of the second core 18, between the wires of each core 16, 18 except for these portions, and furthermore into the gaps between the wires and the first and second covers 17 and 19. When the hot-melt 24 is cured, the hot-melt 24 has a waterproof function. The hot-melt 24 cures by reacting with moisture (humidity) in the air after being heated and melted using, for example, polyurethane-based uncured resin as a major component. In addition, the heat-shrink tube 14 has a property of shrinking generally in the diameter direction when heat is applied thereto, and uses polyolefins, fluorine-based polymer, thermoplastic elastomer, or the like as a material.

(19) Therefore, in the connecting structure for electric cables 11, when drops of water are attached to the connection portion between the terminal 15 made of copper or copper alloy and the core (made of copper or copper alloy) of the copper electric cable, this connection portion is not subjected to contact corrosion because the terminal 15 and the core are made of the same metal. In contrast, the connection portion between the first core 16 of the copper electric cable 12 and the second core 18 of the aluminum electric cable 13 is a connection between heterogeneous metals, and thus is in the danger that corrosion resistance may be caused by drops of water that are attached thereto.

(20) However, according to this embodiment, waterproof ability is realized since the hot-melt 24 sufficiently permeates to the connection portion between a portion of the first core 16 of the copper electric cable 12 and a portion of the second core 18 of the aluminum electric cable 13, to the gap between the first core 16 and the first cover 17 at one end of the first cover 17, and to the gap between the second core 18 and the second cover 19 at one end of the second cover 19. Due to this, it is possible to avoid moisture from being attached to the connection portion, so that contact corrosion does not occur in the connection portion. Here, the hot-melt 24, which is applied on the inner surface of the heat-shrink tube 14, is provided in an amount (thickness) that can be filled, so as to be filled between the wires of each core 16, 18 and in the gaps between the wires and the covers 17 and 19 without being excessive or insufficient.

(21) In this way, this embodiment does not apply the anti-corrosion structure for electric cables to the connection portion between the terminal 15 and the aluminum electric cable 13, which has a complicated structure, unlike the related art. Rather, this embodiment uses the anti-corrosion structure in the connection portion between the copper electric lien 12 and the aluminum electric cable 13, in which connection processing and repair are easy. Although the connecting structure for electric cables according to this embodiment is embodied in order to obtain anti-corrosion effect at the connection portion between the copper electric cable 12 and the aluminum electric cable 13, i.e. the heterogeneous metals, this can also be used in order to obtain waterproof effect at the connection portion between copper electric cables or between aluminum electric cables.

(22) A description will be given below of the sequence of connecting electric cables.

(23) (Connecting Sequence 1)

(24) First, the copper electric cable 12 to be connected to the terminal 15 is prepared. The copper electric cable 12 is short, as shown in FIG. 2. However, the copper electric cable 12 is preferably set to a predetermined length so as to support the heat-shrink tube 14, which is fitted thereon. The copper electric cable 12 is connected and interposed between the terminal 15 and the aluminum electric cable 13. The terminal 15 may be preferably connected to one end of the copper electric cable 12 in advance or after the heat-shrink tube 14 is mounted.

(25) In sequence, the leading end of the first core 16 that is exposed from the first cover 17 of the copper electric cable 12, i.e. the first electric cable, and the leading end of the second core 18 that is exposed from the second cover 19 are set so as to concentrically oppose each other, as shown in FIG. 4A. In addition, the opposing leading ends of the first core 16 and the second core 18 are butted to each other, and as shown in FIG. 4B, the opposing leading ends of the first core 16 and the second core 18 are connected together via cold welding as described above.

(26) Afterwards, the heat-shrink tube 14 shown in FIG. 4C is prepared. The heat-shrink tube 14 has a property of reducing and narrowing in the diameter direction when heat is applied from the outside. The heat-shrink tube 14 has a length that includes a predetermined length of one end of the first cover 17 in the copper electric cable 12 and a predetermined length of one end of the second cover 19 in the aluminum electric cable 13, which oppose each other, and is shaped such that it can surround a portion of the first core 16 and a portion of the second core 18, which are connected to each other, from the surrounding. In addition, the inner diameter of the heat-shrink tube 14 is greater than the outer diameter of the first cover 17 and the second cover 19.

(27) On the inner surface (inner circumference) of the heat-shrink tube 14, the hot-melt 24 shown in FIG. 4D is applied. The thickness of the hot-melt 24 is set to a size such that the hot-melt 24 permeates to the gaps between the wires of the first core 16, between the wires and the first cover 17, between the wires of the second core 18, and between the wires and the second cover 19, thereby filling the gaps without being excessive or insufficient. The inner circumference of the center hole 24a formed by the hot-melt 24 is set to be slightly greater than the outer size of the copper electric cable 12 and the aluminum electric cable 13, such that the copper electric cable 12 and the aluminum electric cable 13 can be smoothly inserted into the first cover 17 and the second cover 19.

(28) In addition, the heat-shrink tube 14 on which the hot-melt 24 is applied has a through-hole so as to cover the first core 16, the second core 18, one end of the first cover 17, and one end of the second cover 19 that is opposite one end of the first cover 17 across a predetermined length. In the process shown in FIG. 4E, the hot-melt 24 is not yet melted, and thus a space 25 is maintained between the first core 16 and the second core 18, which are exposed from the first cover 17 and the second cover 19.

(29) After that, when the heat-shrink tube 14 is heated by, for example, blowing hot wind from the outside of the heat-shrink tube 14, the heat-shrink tube 14 shrinks generally in the diameter direction, as shown in FIG. 4F. At the same time, the hot-melt 24 applied on the inner surface of the heat-shrink tube 14 starts to melt. Then, the viscosity of the hot-melt 24 gradually decreases due to this melting, and the hot-melt 24 starts to flow not only to the outer circumference of the first cover 17 and the second cover 19, which are surrounded by the heat-shrink tube 14, but also to the outer circumference of the first core 16 and the second core 18, which are exposed from the covers 17 and 19.

(30) In addition, as the molten hot-melt 24 is under the shrinking force of the heat-shrink tube 14, the molten hot-melt 24 starts to permeate between the plurality of wires of the first core 16, between the plurality of wires of the second core 18, and further into the gaps between the wires of each core 16, 18 and the first and second covers 17 and 19. Since the hot-melt 24, which is applied on the inner surface of the heat-shrink tube 14, is set to a predetermined sufficient thickness (amount), it permeates at a sufficient density into the region of the first core 16 except for the above-described portion and the region of the second core 18 except for the above-described portion, without leaving a gap.

(31) When the hot-melt 24 is solidified after having sufficiently permeated, the gaps are closed by the hot-melt 24, as shown in FIG. 5, so that the connection portion between the copper electric cable 12 and the aluminum electric cable 13 is in the waterproof state. Therefore, it is possible to prevent contact corrosion from occurring at the connection portion between the copper electric cable 12 and the aluminum electric cable 13, and to control drops of water from flowing (moving) from the aluminum electric cable 13 to the copper electric cable 12, thereby preventing contact corrosion from occurring in the terminal 15 as well as an increase in electrical resistance due to the deterioration of insulation or the production of nest.

(32) (Connecting Sequence 2)

(33) First, as in the connecting sequence 1, the copper electric cable 12 to be connected to the terminal 15 is prepared. Although the copper electric cable 12 is short as shown in FIG. 2, the copper electric cable 12 is preferably set to a predetermined length so as to support the heat-shrink tube 14, which is fitted thereon. The copper electric cable 12 is connected and interposed between the terminal 15 and the aluminum electric cable 13. The terminal 15 may be preferably connected to one end of the copper electric cable 12 in advance or after the heat-shrink tube 14 is mounted.

(34) In sequence, the leading end of the first core 16 that is exposed from the first cover 17 and the leading end of the second core 18 that is exposed from the second cover 19 are set so as to concentrically oppose each other, as shown in FIG. 6A. In addition, the opposing leading ends of the first core 16 and the second core 18 are butted to each other, and as shown in FIG. 6B, are bonded together via cold welding as described above.

(35) Afterwards, as shown in FIG. 6C, the hot-melt 24 is applied to a predetermined thickness (amount) on a region having a predetermined length that is adjacent to the connection portion between the first core 16 and the second core 18, the region including a portion of the first cover 17 and a portion of the second cover 19, and a portion of the outer circumference of the first and second cores 16 and 18, which are exposed from the first and second covers 17 and 19. The thickness of the hot-melt 24 is set to a size such that the hot-melt 24 is melted by heat and permeates to the gaps between the wires of the first core 16, between the wires and the first cover 17, between the wires of the second core 18, and between the wires and the second cover 19, thereby filling the gaps without being excessive or insufficient.

(36) Afterwards, the heat-shrink tube 14 shown in FIG. 6D is prepared. The heat-shrink tube 14 has a property of reducing and narrowing in the diameter direction when heat is applied from the outside. The heat-shrink tube 14 has a length that includes a predetermined length of one end of the first cover 17 in the copper electric cable 12 and a predetermined length of one end of the second cover 19 and in the aluminum electric cable 13, which oppose each other, and is shaped such that it can surround a portion of the first core 16 and a portion of the second core 18, which are connected to each other, from the surrounding. The inner diameter of the heat-shrink tube 14 is set such that the heat-shrink tube 14 can be fitted around the hot-melt 24 with a gap therefrom. Here, the heat-shrink tube 14 is fitted around the first cover 17 or the second cover 19 in advance before the first core 16 and the second core 18 are connected to each other.

(37) Afterwards, the heat-shrink tube 14 is moved along the first cover 17 or the second cover 19 so that it fitted as shown in FIG. 6E so as to surround the entire length of the hot-melt 24.

(38) After that, when the heat-shrink tube 14 is heated by blowing hot wind from the outside of the heat-shrink tube 14, the heat-shrink tube 14 shrinks generally in the diameter direction, as shown in FIG. 6F. At the same time, the hot-melt 24 applied on the inner surface of the heat-shrink tube 14 melts. Then, the viscosity of the hot-melt 24 gradually decreases due to this melting, and the hot-melt 24 starts to flow not only to the outer circumference of the first cover 17 and the second cover 19, which are surrounded by the heat-shrink tube 14, but also to the outer circumference of the first core 16 and the second core 18, which are exposed from the covers 17 and 19.

(39) In addition, as the molten hot-melt 24 is under the shrinking force of the heat-shrink tube 14, the molten hot-melt 24 permeates between the plurality of wires of the first core 16, between the plurality of wires of the second core 18, and further into the gaps between the wires of each core 16, 18 and the first and second covers 17 and 19. Since the thickness of the hot-melt 24 is set to a predetermined size, it sufficiently permeates into the region of the first core 16 except for the above-described portion and the region of the second core 18 except for the above-described portion, without leaving a gap.

(40) After the hot-melt 24 has permeated, the hot-melt 24 is solidified. As shown in FIG. 5, the gaps are closed by the hot-melt 24, so that the connection portion between the copper electric cable 12 and the aluminum electric cable 13 is in the waterproof state. Therefore, it is possible to prevent contact corrosion from occurring at the connection portion between the copper electric cable 12 and the aluminum electric cable 13, and to regulate drops of water from flowing (moving) from the aluminum electric cable 13 to the copper electric cable 12, thereby preventing contact corrosion from occurring in the terminal 15 as well as an increase in electrical resistance due to the deterioration of insulation or the production of rust.

(41) As set forth above, according to the connecting structure and connecting method for connecting electric cables of this embodiment, it is possible to impart a waterproof structure to the gaps between the wires of each core 16, 18 and between the wires and the first and second covers 17 and 19 by allowing the hot-melt 24 to permeate to the region inside the heat-shrink tube 14, which is shrunk with a portion of the connected first and second cores 16 and 18 being accommodated therein, except for a portion of the first and second cores 16 and 18, and then curing the hot-melt. This waterproof structure makes it possible to prevent the contact corrosion from occurring in the connection portion, since drops of water (moisture) do not enter the surrounding of the connection portion between the first core 16 and the second core 18. This effect can be simply obtained using the melting of the hot-melt 24 and the shrinking force of the heat-shrink tube 14.