Title of Invention

ELECTRIC CABLE END PROCESSING METHOD AND ELECTRIC CABLE END STRUCTURE WITH SOLDER COATING AND SHEATH PROTECTION

Technical Field

The present invention is related to an electric cable end processing method for processing an electric cable end to be connected to a connector terminal, and an electric cable end structure.

Background Art

It is conventional a process for soldering of an aluminum electric cable which includes: preliminarily heating aluminum core wires by immersing aluminum core wires in a bath of heated and molten solder; immersing the heated aluminum core wires into a flux bath; subsequently immersing the aluminum core wires again into the solder bath to cause the solder penetrate and adhere to the aluminum core wires; and soldering the aluminum core wires (see, PTL 1). Another conventional process includes applying ultrasonic waves to molten solder in order to eliminate an aluminum oxide layer (see, PTL 2).

Citation List

[Patent Literature]

[PTL 1] JP-A-61- 180674 [PTL 2] J P-A-60- 155664

Summary of Invention

Technical Problem

As shown in Fig. 9, in order to eliminate an oxide layer from an entire exposed portion of aluminum core wires 1 and thereafter coat the aluminum core wires with solder, a sheath 3 located at an end portion of an electric cable 2 must also be immersed in molten solder 4 ultrasonically vibrated by an ultrasonic vibrating plate 5. However, in a case where the sheath 3 is immersed in the molten solder 4 as mentioned above, the sheath 3 will be damaged by heat of the molten solder 4.

In a case where the sheath 3 is not immersed in the molten solder 4, it will be impossible to remove a oxide layer from the entire exposed portion of the core wires 1 and completely coat the exposed portion with solder, so that an uncoated portion where is not coated with solder will be formed. In this case, if the electric cable 2 is connected to a terminal made from copper or a copper alloy, an area where the uncoated portion contacts the terminal will be in a copper-aluminum contact that has severe galvanic corrosion, which may obstruct exhibition of superior corrosion resistance.

It is therefore one advantageous aspect of the present invention to provide an electric cable end processing method for processing an end in such a way that an entire exposed portion of a conductor made from aluminum or an aluminum alloy is coated with solder, as well as providing an electric cable end structure in which the end is processed with the method. Solution to Problem

According to one advantage of the invention, there is provided an end processing method for processing an end of an electric cable including a conductor made from aluminum or an aluminum alloy and a sheath covering the conductor, the end processing method comprising:

removing an end portion of the sheath to expose an end portion of the conductor;

immersing the a part of the exposed end portion of the conductor into molten solder to coat the immersed part of the exposed end portion of the conductor with solder;

providing a heat shrinkable tube through which the conductor is inserted so that a remaining portion of the exposed end portion of the conductor which is not coated with solder is covered by the heat shrinkable tube; and

shrinking the heat shrinkable tube by heating the heat shrinkable tube so as to be close contact with the conductor and the sheath.

In the end processing method, ultrasonic vibrations may be applied to the molten solder into which the conductor is immersed.

According to another advantage of the invention, there is provided an electric cable end structure, comprising:

a conductor made from aluminum or an aluminum alloy;

a sheath covering the conductor; and

a heat shrinkable tube through which the conductor is inserted, wherein an end portion of the conductor is exposed by removing the sheath, a part of the end portion of the conductor including an end of the conductor is coated with solder, and

a remaining part of the end portion of the conductor which is not coated with solder is covered by the heat shrinkable tube so that the heat shrinkable tube is in close contact with the conductor and the sheath.

Advantageous Effects of Invention

Under the electric cable end processing method according to the present invention, the conductor can be coated with solder without damaging the sheath.

Further, the uncoated portion equivalent to the remaining part of the conductor is covered by the heat shrinkable tube, whereby the entire exposed portion of the conductor made from aluminum or an aluminum alloy is coated with solder. Even when the electric cable is connected to a terminal made from copper or a copper alloy, a copper-aluminum contact that has severe galvanic corrosion is not occurred, but a copper-tin contact that has less galvanic corrosion is provided.

Under the electric cable end processing method, molten solder can be ultrasonically vibrated and thereby attached to the exposed portion of the conductor made from aluminum or an aluminum alloy. An oxide layer of the conductor can thereby be removed and well coated with solder. In the electric cable end structure, an exposed portion of the conductor made from aluminum or an aluminum alloy is coated with solder. Accordingly, even when the electric cable is connected to a terminal made from copper or a copper alloy, a copper-aluminum contact that has severe galvanic corrosion is not occurred but a copper-tin contact that has less galvanic corrosion is provided. According to the present invention, it is possible to provide an electric cable end processing method for effecting end process to coat an entire exposed portion of a conductor made from aluminum or an aluminum alloy with solder as well as an electric cable end structure subjected to end process under the method.

Brief Description of Drawings

Fig. 1 is a side view of an end portion of an electric cable to be processed by an electric cable end processing method according to an embodiment of the present invention.

Fig. 2 is a side view showing an electric cable end structure processed by the electric cable end processing method

Fig. 3 is a side view of a connector terminal to which there is connected the end of the electric cable processed by the electric cable processing method.

Fig. 4 is a side view of an electric cable whose core wires are exposed by a normal exposure dimension.

Fig. 5 is a schematic sectional view of an ultrasonic soldering apparatus for explaining a solder coating step.

Fig. 6 is a side view of an electric cable in which core wires are coated with solder.

Fig. 7 is a side view of the electric cable for explaining a tube attachment step. Fig. 8 is a side view of a connector terminal processed by a conventional electric cable end process.

Fig. 9 is a schematic sectional view for explaining a related art example to coat core wires with solder. Description of Embodiments

An exemplary embodiment for implementing the present invention is hereunder described by reference to the drawings.

Fig. 1 is a side view of an end of an electric cable to be processed by an electric cable end processing method of an embodiment of the invention. Fig. 2 is a side view showing an electric cable end structure processed by the electric cable end processing method of the embodiment. Fig. 3 is a side view of a connector terminal to which there is connected the end of the electric cable processed by the electric cable processing method of the embodiment. Fig. 4 is a side view of an electric cable whose core wires are exposed by a normal exposure dimension. Fig. 5 is a schematic sectional view of an ultrasonic soldering apparatus for explaining a solder coating step. Fig. 6 is a side view of an electric cable in which core wires are coated with solder. Fig. 7 is a side view of the electric cable for explaining a tube attachment step.

As shown in Fig. 1 , an electric cable 11 to be processed has core wires (conductor) 12 made of conductive material and a sheath 13 made of insulative material and extruded so as to cover a periphery of the core wires 12. The core wires 12 may be made from aluminum or an aluminum alloy for instance. The sheath 13 may be formed from resin.

As shown in Fig. 2, the sheath 13 is removed from an end portion of the electric cable 11 so as to expose the core wires 12. The exposed portion of the core wires 12 are coated with solder 14. Moreover, the electric cable 11 is covered by a tube 5 so that an area between a portion coated with the solder 14 and the sheath 13 is covered. In addition, the area is an uncoated portion in the exposed portion of the core wires 12 which is not coated with solder. The tube 5 is made from a heat shrinkable tube and held in close contact with the core wires 12 of the electric cable 11 and an outer peripheral surface of the sheath 13.

As shown in Fig. 3, the electric cable 11 which is processed as mentioned above is connected to the connector terminal 10. The connector terminal 10 is made of conductive metallic material. The connector terminal 10 may be formed from copper or a copper alloy that is a conductive metallic material and be formed by means of pressing for instance. The connector terminal 10 has a barrel 21 and a tab terminal section 31. The barrel 21 has a core wire crimping section 22 and a sheath crimping section 23. The core wire crimping section 22 crimps the core wires 12 exposed at the end portion of the electric cable 1 . The core wires 2 of the electric cable and the connector terminal 10 are conductively connected to each other. The sheath crimping section 23 crimps a part of the sheath 13 situated at the end portion of the electric cable 11. The sheath 13 of the electric cable 11 is fastened to the connector terminal 10.

The tab terminal section 31 is an area to which a tab of the connector terminal is to be connected. A tab of the counterpart connector terminal is connected to the tab terminal section 31 , whereby the connector terminal 10 is brought into electrical conduction with the connector terminal.

The electric cable end processing method will be explained. First, as shown in Fig. 1 , in a step of removing, the sheath 13 at the end portion of the electric cable 11 is cut and thereafter removed from, to expose the core wires 12. An exposed dimension L that is a dimension of the electric wires 2 to be exposed in its axial direction by removing the sheath 13 is set to a slightly long dimension beforehand. As shown in Fig. 4, the exposed dimension L of the core wires 12 is longer than a normal exposed dimension Ln that is sufficient to crimp the core wires 12 to the core wire crimping section 22 of the barrel 21 of the connector terminal 10. The exposed dimension L is also a length which the core wires 12 do not contact the sheath crimping section 23 of the barrel 21 in a state where the core wires 12 are crimped to the core wire crimping section 22.

Next, in a step of coating, the exposed portion of the core wires 12 are coated with the solder 14. As shown in Fig. 5, an ultrasonic soldering apparatus 41 is used in the present embodiment. The ultrasonic soldering apparatus 41 has a solder bath 42 that stores molten solder 14a, and an ultrasonic vibrating plate 43 is disposed in the solder bath 42. The ultrasonic vibrating plate 43 is ultrasonically vibrated by an ultrasonic transducer (omitted from the drawings). As a result of the ultrasonic vibrating plate 43 being ultrasonically vibrated, ultrasonic vibrations are propagated to the molten solder 14a in the solder bath 42. In order to coat the core wires 12 with the solder 14 by use of the ultrasonic soldering apparatus 41 , a part of the exposed portion of the core wires 12 is immersed from above into the molten solder 14a stored in the solder bath 42. In this immersing process, the sheath 13 is prevented from contacting the molten solder 14a. A dimension of the immersed part of the core wires 12 is set to a dimension that is slightly longer than the normal exposed dimension Ln.

As mentioned above, after the core wires 12 are immersed into the molten solder 14a stored in the solder bath 42, the ultrasonic vibrating plate 43 is ultrasonically vibrated by the ultrasonic transducer. As a result of this, an oxide layer formed over a surface of each of the core wires 12 is removed by the ultrasonic vibrations. The molten solder 14a spreads to the immersed part of the exposed portion and to interior potions of the core wires 12, whereupon a coating of the solder 14 is favorably formed. Moreover, in the step of immersing, the ultrasonic vibrating plate 43 is ultrasonically vibrated while the electric cable 11 is pressed toward the solder bath 42 so that the core wires 12 are held in contact with the ultrasonic vibrating plate 43. Thereby, the ultrasonic vibration is certainly propagated to the core wires 2, so that the molten solder 14a can spread to the immersed part of the exposed portion and the interior portions of the core wires 2 between respective strands of the core wires 12.

Further, by a part of the exposed portion of the core wires 12 is immersed in the molten solder 14a in such a way that the sheath 13 does not contact the molten solder 14a, damage to the sheath 13 from the heat of the solder 14, which would otherwise be caused by the molten solder 14a, is prevented. As shown in Fig. 6, the immersed part of the exposed portion of the core wires 12 of the electric cable 1 which is coated with the solder 14 by the step of immersing has a length of a dimension La that is slightly longer than the normal exposed dimension Ln. Further, an uncoated portion 16 which is not coated with the solder 14 is formed between the immersed part and the sheath 13.

In a step of providing of the tube 15, the tube 15 is attached to the electric cable 11 in which the immersed portion of the core wires 12 is coated with the solder 14 as mentioned above.

Specifically, a leading end of the electrical wire 11 is inserted into the tube 15 which is not shrunk, and the tube 15 is arranged so as to cover the uncoated portion 16 of the core wires 12 and straddle between the immersed portion of the core wires 12 and the sheath 13. The tube 15, in this state, is heated and thereby shrunk. Thereupon, the tube 15 closely contacts the core wires 12 and the sheath 13. Therefore, as shown in Fig. 2, the uncoated portion 16 of the core wires 12 are covered by the tube 15. In the electric cable 1 processed as mentioned above, an entire part of the core wires 12 which is not covered by the tube 15 and the sheath 13is coated with the solder 4. Therefore, when the connector terminal 0 is connected by crimping the core wires 12 of the electric cable 11 to the core wire crimping section 22 and crimping the sheath 13 to the sheath crimping section 23, the connector terminal 0 made from copper or a copper alloy comes into contact with the solder 14 including tin as the main ingredient, in the core wire crimping section 22.

Galvanic corrosion may occur in a contact between dissimilar metals contact. The galvanic corrosion is corrosion that occurs when a conductive liquid exists in a contact between dissimilar metals. Influence of the galvanic corrosion becomes greater as a potential difference between dissimilar metals increases. Since a copper-tin contact is smaller than a copper-aluminum contact in terms of a potential difference, the galvanic corrosion can be lessened in accordance with the embodiment of the invention.

Specifically, in the electric cable 11 processed by the end processing method of the present embodiment, an area of electrical conduction between the connector terminal 0 and the electric cable 11 can be realized as a copper-tin contact that will induce less severe galvanic corrosion.

As described above, in the present embodiment, the core wires 12 can be coated with the solder 14 without inflicting damage to the sheath 3. Further, the uncoated portion 16 of the core wires 2 is covered by the tube 15, whereby the entire uncovered portion of the core wires 12 made from aluminum or an aluminum alloy is coated with the solder 14. Even when the electric cable 11 is connected to the connector terminal 10 made from copper or a copper alloy, a resultant contact does not turn into a copper-aluminum contact that will induce severe galvanic corrosion but instead into a copper-tin contact that will induce less severe galvanic corrosion. Moreover, waterproof of clearance between the core wires 12 and the sheath 13 can also be assured by means of the tube 15. Furthermore, the electric cable 11 can be shipped in the form of a product in which the core wires 12 are coated with the solder 14 in advance and in which the uncoated portion 16 is covered with the tube 15. Thus, an attempt can be made to simplify operation in subsequence steps. The molten solder 14 can be applied to the immersed portion of the core wires

12 made from aluminum or aluminum alloy, by means of ultrasonic vibration. An oxide layer of the core wires 12 can be removed, and therefore the core wires 12 can be favorably coated with the solder 14. A related art of the electric cable end processing method will be explained by referring Figs. 4 and 8 for clarify difference from the embodiment of the present invention.

In Fig. 4, the core wires 12 is exposed by the normal exposed dimension Ln and merely coated with the solder 14. In this case, as shown in Fig. 8, the electric cable 11 is connected to the connector terminal 10 while the uncoated portion 16 is not covered. The connector terminal 10 made from copper or a copper alloy and the core wires 12 made from aluminum or an aluminum alloy eventually come into direct contact with each other. A copper-aluminum contact that will induce severe galvanic corrosion occurs between the connector terminal 10 and the core wires 12.

If the uncoated portion 16 where an oxide layer still remains exists in a crimp area of the core wire crimping section 22, conductivity may also be deteriorated.

The above-mentioned embodiment is merely a typical example of the present invention, and the present invention is not limited to the embodiment. That is, the present invention can be variously modified and implemented without departing from the essential features of the present invention.

The present application is based on Japanese Patent Application No. 2011-187629 filed on August 30, 2011 , the contents of which are incorporated herein by way of reference.

Industrial Applicability

According to the electric cable end processing method, there is provided an electric cable end structure in which an entire exposed portion of a conductor made from aluminum or an aluminum alloy is coated with solder.

Reference Signs List

11 ELECTRIC CABLE

12 CORE WIRE (CONDUCTOR)

13 SHEATH

14 SOLDER

14a MOLTEN SOLDER

15 TUBE

16 UNCOATED PORTION