Patent Description:
As an electric wire connection structure formed by interconnecting electric wires to each other for electrical connection, there is a wire harness being routed in an automobile, for example, for power supply and signal transmission. Some wire harnesses are quite long, and when power is fed to each device from one power source, for example, if wiring from one power source is provided on a one-by-one basis, the number of wires increases to cause an increase in weight. Therefore, an electric wire routed is usually formed by one thick wire in a part from a connecting position with a power source to a position close to (a position in front of) each device and is branched to plural thin wires using a joint in the vicinity of each device from the viewpoint of weight reduction. Further, it is useful to use an aluminum-based material having a light weight as a conductor forming an electric wire instead of a copper-based material.

As a joining method, a so-called resistant welding method in which a part to be welded is sandwiched by two electrodes, current is supplied thereto, and metals are joined to each other utilizing heat generated by electric resistance and pressurizing force may be used, for example.

The resistant welding method can relatively easily form a sound joint part when conductor metals of electric wires to be joined are both copper-based materials. However, in a case where metals of different kinds like an Al-based conductor and a Cu-based conductor, for example, are joined with each other, a sound joint part cannot be formed, because only the Al conductor having a lower melting point melts and the Cu conductor having a higher melting point does not melt. Therefore, in order to join metals of different kinds with different melting points by the resistant welding method, the metals should be heated to a high temperature not less than any of melting points of respective metals to be joined in a short time, and joining conditions are difficult to be controlled. In addition, there is a problem in safety because of the high temperature heating.

Therefore, an ultrasonic joining method capable of joining at normal temperature is usually used for joining different kinds of metals with each other. For example, Patent Literature <NUM> describes a wire harness in which strands forming a conductor of an insulated electric wire are joined with each other and a strand and a metal sleeve (or metal foil, etc.) are joined. Patent Literature <NUM> describes an electric wire connection structure in which a joint part is provided at a conductor stacked part in which a copper-based conductor exposed part and an aluminum-based conductor exposed part are superposed. Further prior art is disclosed in Patent Literature <NUM>.

In addition, a case where a copper-based conductor and an aluminum-based conductor are directly ultrasonically joined in a state of being superposed without using a metal sleeve is also supposed from the viewpoint of reducing the number of parts forming a wire harness.

However, when a copper-based conductor and an aluminum-based conductor are superposed and ultrasonically joined, depending on a combination of conductor materials different from one other for the copper-based conductor and the aluminum-based conductor or according to change of joining conditions or the like, a defect part (a space) at which the conductors are not joined (not in contact) may become prone to be present at a joint interface between the copper-based conductor and the aluminum-based conductor forming an ultrasonic joint part. In such a case, there is a problem that a part of the aluminum-based conductor is anodically dissolved due to crevice corrosion, and an increase in electric resistance and a decrease in joining strength (pull-out strength) are easily caused.

An object of the present invention is to provide an electric wire connection structure in which an increase in electric resistance and a decrease in joining strength (pull-out strength) caused by crevice corrosion are effectively suppressed by optimizing characteristics of a joint interface of an ultrasonic joint part formed by a copper-based conductor exposed part and an aluminum-based conductor exposed part.

The object is satisfied by an electric wire connection structure in accordance with the features of claim <NUM>. Preferred embodiments of the present invention are disclosed in the dependent claims. As a result of intensively studying on the above problem, the present inventors have found that an increase in electric resistance and a decrease in joining strength (tensile strength) caused by crevice corrosion can be effectively suppressed in the following manner. In order to form an ultrasonic joint part with a copper-based conductor exposed part and an aluminum based conductor exposed part, one conductor exposed part out of the copper-based conductor exposed part and the aluminum-based conductor exposed part is made of a material more deformable than the other conductor exposed part, and preferably, conductors made of materials with a difference in tensile strength therebetween being <NUM> MPa or more are used in combination for a copper-based conductor and an aluminum-based conductor. Resulting configuration allows one conductor exposed part to be relatively significantly collapsed and easily plastically fluidized by pressurizing force during ultrasonic joining, and therefore, one conductor exposed part enters to a space unjoined (not in contact), which is likely to be formed between the copper-based conductor exposed part and the aluminum-based conductor exposed part forming a joint interface, through plastic flow to fill the space. As a result, formation of an ultrasonic joint part having a sound joint interface is made possible. The present invention has been completed thereby.

According to the present invention, provision of an electric wire connection structure in which an increase in electric resistance and a decrease in joining strength (pull-out strength) caused by crevice corrosion are effectively suppressed has become possible by an electric wire connection structure in accordance with the present invention.

Hereinafter, embodiments according to the present invention will be described with reference to drawings below. <FIG> is a perspective diagram of an electric wire connection structure of one embodiment according to the present invention. The shown electric wire connection structure <NUM> includes one or more copper-based conductor covered electric wires <NUM> having a copper-based conductor covered part <NUM> and a copper-based conductor exposed part <NUM> and one or more aluminum-based conductor covered electric wires <NUM> having an aluminum-based conductor covered part <NUM> and an aluminum-based conductor exposed part <NUM>. In addition, the electric wire connection structure <NUM> has an ultrasonic joint part <NUM> provided at a conductor stacked part in which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are superposed.

The electric wire connection structure <NUM> of the present invention includes one or more copper-based conductor covered electric wires <NUM> having the copper-based conductor covered part <NUM> in which a copper-based conductor made of copper or a copper alloy is covered with an insulating cover and the copper-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the copper-based conductor; and one or more aluminum-based conductor covered electric wires <NUM> having the aluminum-based conductor covered part <NUM> in which an aluminum-based conductor made of aluminum or an aluminum alloy is covered with an insulating cover and the aluminum-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the aluminum-based conductor, and the electric wire connection structure <NUM> includes a joint part provided at a conductor stacked part in which the copper-based conductor exposed part and the aluminum-based conductor exposed part are superposed, with a joint interface of the joint part being provided by the aluminum-based conductor covered electric wire being melted so as to fill a gap of the copper-based conductor covered electric wire based on cross-section observation.

In addition, the electric wire connection structure <NUM> of the present invention includes one or more copper-based conductor covered electric wires <NUM> having the copper-based conductor covered part <NUM> in which a copper-based conductor made of copper or a copper alloy is covered with an insulating cover and the copper-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the copper-based conductor; and one or more aluminum-based conductor covered electric wires <NUM> having the aluminum-based conductor covered part <NUM> in which an aluminum-based conductor made of aluminum or an aluminum alloy is covered with an insulating cover and the aluminum-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the aluminum-based conductor, and the electric wire connection structure <NUM> includes an ultrasonic joint part provided at a conductor stacked part in which the copper-based conductor exposed part and the aluminum-based conductor exposed part are superposed, with a joint interface of the ultrasonic joint part satisfying a relational expression of (x/L) × <NUM> ≤ <NUM>% where a total contacting length which is a summed length of a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part contact is L and a summed length of a contour line of a space formed at a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part are separate is x based on cross-section observation. Each element forming the electric wire connection structure <NUM> is as follows, and the electric wire connection structure <NUM> like this can effectively suppress an increase in electric resistance and a decrease in joining strength (pull-out strength) caused by crevice corrosion.

The copper-based conductor covered electric wire <NUM> used in the present invention has the copper-based conductor covered part <NUM> in which a copper-based conductor made of copper or a copper alloy is covered with an insulating cover and the copper-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the copper-based conductor. The copper-based conductor covered electric wire <NUM> may be one covered electric wire in which a copper-based conductor formed by bundling plural strands made of a copper-based material is covered with an insulating cover or may be plural covered electric wires formed by bundling such covered electric wires, for example. In addition, while it is preferable that the copper-based conductor is formed by twisting strands to have a predetermined cross-sectional area, the copper-based conductor is not limited to this form and may be formed by a single wire. A strand diameter and the number of strands forming the copper-based conductor are not particularly limited, but it is preferable that the diameter of a strand is within a range of <NUM> to <NUM> and the number of strands is within a range of <NUM> to <NUM>, for example.

The copper-based conductor is not particularly limited, but pure copper such as tough pitch copper, oxygen-free copper, and phosphorous-deoxidized copper, brass, phosphor bronze, a corson-type copper alloy (Cu-NiSi-based alloy), and the like may be used, for example.

As such copper or a copper alloy, pure copper of alloy number C1000 series, a Cu-Zn-based alloy of alloy number C2000 series, a Cu-Sn-based alloy of alloy number C5000 series, and a Cu-Al-based alloy of alloy number C6000 series according to the standard of JIS H <NUM>:<NUM> can be used, for example.

The insulating cover is not particularly limited as long as it is a material having insulation properties, but a halogen-based resin containing polyvinyl chloride, crosslinked polyvinyl chloride, chloroprene rubber, or the like as a main component or a halogen-free resin containing polyethylene, crosslinked polyethylene, ethylene propylene rubber, silicone rubber, polyester, or the like as a main component, and the like can be used as a resin material forming the insulating cover, for example, and a polyvinyl chloride resin is especially used. In addition, an additive such as a plasticizer, a flame retardant, and the like may be included in these resin materials as needed.

The copper-based conductor covered part <NUM> represents a part of the copper-based conductor where the copper-based conductor is not exposed and covered with the insulating cover in the copper-based conductor covered electric wire <NUM> in which the copper-based conductor is covered with the insulating cover. The copper-based conductor covered part <NUM> is a part of the original copper-based conductor free from an influence from ultrasonic waves described later.

The copper-based conductor exposed part <NUM> represents a part where the copper-based conductor is exposed by stripping a part of the insulating cover by a predetermined length. The copper-based conductor exposed part <NUM> is a part of the copper-based conductor to which ultrasonic waves are applied as described later, and forms the ultrasonic joint part <NUM> together with the aluminum-based conductor exposed part <NUM> responding to ultrasonic waves. The length of the insulating cover to be stripped is not particularly limited as long as the copper-based conductor exposed part <NUM> has a length enough to be ultrasonically joined with the aluminum-based conductor exposed part <NUM>, and the length of the insulating cover to be stripped can be appropriately set according to the range of a region to be joined with the corresponding aluminum-based conductor exposed part <NUM>. The length of the copper-based conductor exposed part <NUM>, that is, the length of the insulating cover to be stripped is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>, for example.

The aluminum-based covered electric wire <NUM> used in the present invention has the aluminum-based conductor covered part <NUM> in which an aluminum-based conductor is covered with an insulating cover and the aluminum-based conductor exposed part <NUM> in which a part of the insulating cover is stripped by a predetermined length to expose the aluminum-based conductor. The aluminum-based covered electric wire <NUM> may be one covered electric wire in which an aluminum-based conductor formed by bundling plural strands made of an aluminum-based material is covered with an insulating cover or may be plural covered electric wires formed by bundling such covered electric wires, for example. In addition, while it is preferable that the aluminum-based conductor is formed by twisting strands to have a predetermined cross-sectional area, the aluminum-based conductor is not limited to this form and may be formed by a single wire. A strand diameter and the number of strands forming the aluminum-based conductor are not particularly limited, but it is preferable that the diameter of a strand is within a range of <NUM> to <NUM> and the number of strands is within a range of <NUM> to <NUM>, for example.

The aluminum-based conductor is not particularly limited, but pure aluminum (Al) and aluminum alloys such as an aluminum-manganese-based alloy (Al-Mn-based alloy), an aluminum-magnesium-based alloy (Al-Mg-based alloy), an aluminum-magnesium-silicon-based alloy (Al-Mg-Si-based alloy), an aluminum-zinc-magnesium-based alloy (Al-Zn-Mg-based alloy), and an aluminum-copper-magnesium-based alloy (Al-Cu-Mg alloy) can be used, for example. An aluminum alloy is preferable from the viewpoint of imparting higher strength.

As such aluminum or an aluminum alloy, pure aluminum of alloy number <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, an Al-Mn-based alloy of alloy number <NUM> or <NUM>, an Al-Mg-based alloy of alloy number <NUM>, <NUM>, <NUM>, or <NUM>, an Al-Mg-Si-based alloy of alloy number <NUM>, 6N01, 6005A, <NUM>, <NUM>, <NUM>, or <NUM>, an Al-Zn-Mg-based alloy of alloy number <NUM>, 7N01, <NUM>, <NUM>, <NUM>, or <NUM>, and an Al-Cu-Mg alloy of alloy number <NUM>, 2014A, <NUM>, 2017A, or <NUM> according to the standard of JIS H <NUM>:<NUM> can be used, for example.

The aluminum-based conductor covered part <NUM> represents a part of the aluminum-based conductor where the aluminum-based conductor is not exposed and covered with the insulating cover in the covered electric wire <NUM> in which the aluminum-based conductor is covered with the insulating cover. The aluminum-based conductor covered part <NUM> is a part of the original aluminum-based conductor free from an influence from ultrasonic waves described later.

The aluminum-based conductor exposed part <NUM> represents a part where the aluminum-based conductor is exposed by stripping a part of the insulating cover by a predetermined length. The aluminum-based conductor exposed part <NUM> is a part of the aluminum-based conductor to which ultrasonic waves are applied as described later, and forms the ultrasonic joint part <NUM> together with the copper-based conductor exposed part <NUM> responding to ultrasonic waves. The length of the insulating cover to be stripped is not particularly limited as long as the aluminum-based conductor exposed part <NUM> has a length enough to be joined with the copper-based conductor exposed part <NUM>, and the length of the insulating cover to be stripped can be appropriately set according to the range of a region to be joined with the corresponding copper-based conductor exposed part <NUM>. The length of the aluminum-based conductor exposed part <NUM>, that is, the length of the insulating cover to be stripped is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>, for example.

The electric wire connection structure <NUM> of the present invention has the ultrasonic joint part <NUM> formed by the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM>. In addition, the ultrasonic joint part <NUM> can be integrally formed by further including a joint tube <NUM> at an outer peripheral side of the conductor stacked part at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are superposed. <FIG> shows a sectional photograph of an electric wire connection structure having an ultrasonic joint part <NUM> provided with a joint tube <NUM> at the outer peripheral side of the conductor stacked part.

Then, a major constitutional feature of the present invention is to optimize characteristics of the joint interface of the ultrasonic joint part <NUM> provided by ultrasonic joining, and in particular to satisfy the relational expression of (x/L) × <NUM> ≤ <NUM>% where a total contacting length which is a summed length of a part at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> contact (join) is L and a summed length of a contour line of a space S formed at a part at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are separate is x based on cross-section observation of the ultrasonic joint part <NUM>, and an increase in electric resistance and a decrease in joining strength (tensile strength) caused by crevice corrosion are effectively suppressed thereby.

Here, the reason why the total contacting length L and the summed length x of the contour line of the space are made to satisfy the relational expression of (x/L) × <NUM> ≤ <NUM>% is that when a value of (x/L) × <NUM> is larger than <NUM>%, the part which is present at the joint interface of the ultrasonic joint part <NUM> and at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are separate increases, the space which causes generation of crevice corrosion increases in its number or volume, and an increase in electric resistance and a decrease in joining strength (pull-out strength) become remarkable.

<FIG> is a diagram diagrammatically illustrating the ultrasonic joint part of <FIG>, <FIG> is an enlarged diagram illustrating the ultrasonic joint part of <FIG> with dashed-two dotted lines and representing with solid lines the part which is present at the joint interface between the aluminum-based conductor exposed part and the copper-based conductor exposed part and at which both exposed parts contact (join), <FIG> is an enlarged diagram illustrating the ultrasonic joint part of <FIG> with dashed-two dotted lines and representing with solid lines spaces S (three spaces in <FIG>) which are present at the joint interface between the aluminum-based conductor exposed part and the copper-based conductor exposed part and which are formed at the part at which the exposed parts are separate from each other, and <FIG> is a diagram for describing a measurement method of the total contacting length L of the contacting part shown in <FIG> and the summed length x of the contour lines of the spaces S shown in <FIG>.

Here, the "total contacting length L" is a summed length of the part which is present at the joint interface between the aluminum-based conductor exposed part <NUM> and the copper-based conductor exposed part <NUM> and at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> contact (join) based on cross-section observation of the ultrasonic joint part <NUM>, and specifically means the total sum of the lengths of the solid lines shown in <FIG>.

In addition, the "summed length x of a contour line of a space" is a summed length of a contour line of a space S formed at a part which is present at the joint interface between the aluminum-based conductor exposed part <NUM> and the copper-based conductor exposed part <NUM> and at which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are separate based on cross-section observation of the ultrasonic joint part <NUM>, and specifically means, when the space S is present at only one location, a contour line length measured for the space S, and when the space S is present at plural locations (three locations in <FIG>) as shown by the solid lines in <FIG>, the total sum of the contour lengths measured for spaces S at the respective plural locations.

Incidentally, measurements on the total contacting length L and the summed length x of the contour line of the space were conducted by a method in which a cross-section of the ultrasonic joint part <NUM> is captured by using an optical microscope or an electron microscope and an extending shape of the joint interface (illustrated by the solid line in <FIG>) can be approximated as much as possible from the captured image or photograph, for example, by a method in which plural straight lines each having a length of <NUM> or less (for example, <NUM>) are used and connected in a line graph as illustrated in <FIG>.

In addition, in the electric wire connection structure of the present invention, it is preferable that a difference in tensile strength between the copper-based conductor and the aluminum-based conductor is <NUM> MPa or more. Consequently, a material of one conductor exposed part (for example, the aluminum-based conductor exposed part <NUM>) out of the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> can be made deformable compared with the other conductor exposed part (for example, the copper-based conductor exposed part <NUM>), and therefore, by combining these conductors with each other, resulting configuration allows one conductor exposed part to be relatively significantly collapsed by pressurizing force during ultrasonic joining, and the one conductor exposed part is preferentially plastically deformed or melted in the space S unjoined (not in contact) which is likely to be formed between the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> forming the joint interface to fill the space S (gap). As a result, formation of an ultrasonic joint part having a sound joint interface is made possible, and an increase in electric resistance and a decrease in joining strength (pull-out strength) caused by crevice corrosion can be more effectively suppressed.

Incidentally, measurements of tensile strength were conducted three times, and an average value thereof was obtained according to JIS Z <NUM>.

Incidentally, in the electric wire connection structure of the present invention, tensile strength may be higher in the aluminum-based conductor than in the copper-based conductor or may be higher in the copper-based conductor than in the aluminum-based conductor to the contrary as long as the difference in tensile strength between the copper-based conductor and the aluminum-based conductor is <NUM> MPa or more, and therefore, a combination of the copper-based conductor and the aluminum-based conductor can be appropriately selected according to application.

Next, a manufacturing method of the electric wire connection structure <NUM> according to the present invention will be described. The manufacturing method of the electric wire connection structure <NUM> in the present invention at least includes a step of mainly preparing a copper-based conductor covered electric wire <NUM> and an aluminum-based conductor covered electric wire <NUM>, a step of forming a copper-based conductor exposed part and an aluminum-based conductor exposed part, and a step of ultrasonically joining the copper-based conductor exposed part and the aluminum-based conductor exposed part to form an ultrasonic joint part.

First, the copper-based conductor covered electric wire <NUM> having a copper-based conductor covered part <NUM> in which a copper-based conductor is covered with an insulating cover and an aluminum-based conductor covered electric wire <NUM> having an aluminum-based conductor covered part <NUM> in which an aluminum-based conductor is covered with an insulating cover are prepared. For the copper-based conductor and the insulating cover forming the copper-based conductor covered electric wire <NUM> and for the aluminum-based conductor and the insulating cover forming the aluminum-based conductor covered electric wire <NUM>, the materials described above can be respectively used, and it is preferable that the insulating cover is a polyvinyl chloride resin. In addition, the copper-based conductor is not particularly limited, but a copper-based conductor formed by twisting and bundling plural strands made of a copper-based material is preferable. For example, a copper-based conductor formed by twisting and bundling seven copper-based strands and having a size (thickness) of <NUM> sq (<NUM><NUM>) can be used. In addition, the aluminum-based conductor is not particularly limited, but an aluminum-based conductor formed by twisting and bundling plural strands made of an aluminum-based material is preferable. For example, an aluminum-based conductor formed by twisting and bundling seven aluminum-based strands and having a size (thickness) of <NUM> sq (<NUM><NUM>) can be used.

Thereafter, the copper-based conductor covered electric wire and the aluminum-based conductor covered electric wire respectively form a copper-based conductor exposed part <NUM> and an aluminum-based conductor exposed part <NUM> each of which is exposed by stripping a part of the insulating cover in a predetermined length. A method for stripping the insulating cover is not particularly limited, but a tool or an instrument such as a wire stripper can be used, for example. The length of the insulating cover to be stripped in each of the covered electric wires <NUM> and <NUM> is appropriately designed according to the range of a region of each of the conductor exposed parts <NUM> and <NUM> to be ultrasonically joined, and the length of the insulating cover to be stripped is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>, for example.

Further, the ultrasonic joint part <NUM> is formed by ultrasonically joining the formed copper-based conductor exposed part <NUM> and aluminum-based conductor exposed part <NUM> in a state of being superposed. In addition, the ultrasonic joint part <NUM> may be formed by inserting an outer peripheral side of a conductor stacked part in which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are superposed to the inside of a joint tube <NUM> and subsequently ultrasonically joining these while applying pressure from an outer surface side of the joint tube <NUM>.

Incidentally, superposition of the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> may be achieved by preliminarily joining a bundle of strands forming the copper-based conductor exposed part <NUM> and a bundle of strands forming the aluminum-based conductor exposed part <NUM> and superposing the joined conductor exposed parts <NUM> and <NUM> with each other.

The ultrasonic joining is conducted by applying parallel ultrasonic vibration to a joint surface <NUM> between the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> while applying pressurizing force in a vertical direction in a state in which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> are superposed. Generally, aluminum is known to form a tough oxide coating on its surface once being exposed to oxygen in the air. In addition, dirt derived from a substance such as oil or dust adheres to a metal surface in some cases. Interfaces between the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> rub against each other by friction caused by ultrasonic vibration to remove an oxide coating and an adhered substance on the joint surface <NUM>, and activated metal molecules appear on a clean joint surface. On further applying ultrasonic vibration, motion of metal atoms becomes active due to heating with frictional heat to cause movement of metal atoms caused by diffusion. Thereafter, strong attracting force is mutually generated between the metal parts, and copper-based metal in the copper-based conductor exposed part <NUM> and aluminum-based metal in the aluminum-based conductor exposed part <NUM> are joined in a solid state.

Since copper-based metal in the copper-based conductor exposed part <NUM> and aluminum-based metal in the aluminum-based conductor exposed part <NUM> are joined in a solid state, temperature rises not so high as to cause both metals to melt, and such ultrasonic joining can be conducted at a relatively low temperature (usually, about <NUM> to <NUM>% of melting points of mother materials). Meanwhile, when parallel ultrasonic vibration is applied to the joint surface <NUM> between the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM>, microscopic shear deformation due to ultrasonic vibration is generated, and consequently, the ultrasonic joint part <NUM> formed by the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> is formed.

<FIG> is a schematic diagram for describing steps of superposing the copper-based conductor covered electric wire <NUM> and the aluminum-based conductor covered electric wire <NUM> and subsequently ultrasonically joining an interface of the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> in that state using an ultrasonic joining apparatus <NUM> to form the ultrasonic joint part <NUM> having the joint surface <NUM>.

As illustrated in <FIG>, for example, shape retention by the ultrasonic joining apparatus <NUM> is performed by placing the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> in a state of being superposed between a pressurizing surface of a horn <NUM> and a pressurizing surface of an anvil <NUM>, clipping the superposed copper-based conductor exposed part <NUM> and aluminum-based conductor exposed part <NUM> with the horn <NUM> and the anvil <NUM> from a vertical direction, and disposing work holding jigs (grinding jaws) <NUM> at both right and left sides so that the superposed state does not collapse. Thereafter, the ultrasonic joining apparatus <NUM> can conduct ultrasonic joining by allowing the horn <NUM> to oscillate ultrasonic vibration oscillating in a longitudinal direction X (arrow A1 in <FIG>) while applying pressure to press in a pressurizing direction Z (arrow A2 in <FIG>) with the anvil <NUM>. Energy of the ultrasonic waves to be applied is not particularly limited but is preferably <NUM> to <NUM> Ws (J) and more preferably <NUM> to <NUM> Ws. In addition, a compression rate of the ultrasonic joint part is preferably in a range of <NUM> to <NUM>%. Incidentally, the "compression rate" herein means a value obtained by dividing a decreased amount from a cross-sectional area before crimping by the cross-sectional area before crimping and multiplying it by <NUM>.

As the ultrasonic joining apparatus <NUM> operates in this way, the ultrasonic vibration oscillated from the horn <NUM> propagates through the inside of one conductor exposed part (the copper-based conductor exposed part <NUM> in <FIG>) in the pressurizing direction Z (arrow A31 in <FIG>) and consequently propagates through the inside of the other conductor exposed part (the aluminum-based conductor exposed part <NUM> in <FIG>) in the pressurizing direction Z (arrow A32 in <FIG>) from the copper-based conductor exposed part <NUM> via an interface to be the joint surface <NUM> to form the joint surface <NUM> around the interface. As a result, the ultrasonic joint part <NUM> is formed. At this time, the joint interface of the ultrasonic joint part can effectively suppress an increase in electric resistance and a decrease in joining strength (pull-out strength) caused by crevice corrosion by a total contacting length L and a summed length x of a contour line of a space S satisfying the relational expression of (x/L) × <NUM> ≤ <NUM>%.

Incidentally, the embodiments described above only exemplify several exemplary embodiments of the present invention, and various modifications can be made within the scope of the present invention.

The present invention will be described in more detail based on the following examples, but the present invention is not limited to these examples.

A copper-based conductor covered electric wire <NUM> and an aluminum-based conductor covered electric wire <NUM> were prepared by covering a copper-based conductor having the composition, tensile strength, and the like shown in Table <NUM> with an insulating cover of polyvinyl chloride and by covering an aluminum-based conductor having the composition, tensile strength, and the like shown in Table <NUM> with an insulating cover of polyvinyl chloride, respectively. Thereafter, the tip side of each of the covered electric wires <NUM>, <NUM> was stripped by about <NUM> by a wire stripper to form a copper-based conductor exposed part <NUM> in which the copper-based conductor was exposed and an aluminum-based conductor exposed part <NUM> in which the aluminum-based conductor was exposed. The copper-based conductor exposed part <NUM> of the copper-based conductor covered electric wire <NUM> and the aluminum-based conductor exposed part <NUM> of the aluminum-based conductor covered electric wire <NUM> thus formed were superposed and subsequently placed on a pedestal (horn side) of an ultrasonic joining apparatus (manufactured by Schunk GmbH) in a state of being superposed. Incidentally, with respect to Examples <NUM> to <NUM>, the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> were placed on the pedestal (horn side) of the ultrasonic joining apparatus with a joint tube disposed at an outer peripheral side of the conductor stacked part in which the copper-based conductor exposed part <NUM> and the aluminum-based conductor exposed part <NUM> of the aluminum-based conductor covered electric wire <NUM> were superposed. Thereafter, ultrasonic waves were applied to the outer surface of the placed conductor stacked part or the outer surface of the joint tube in a state of being sandwiched by the horn and the anvil under the joining conditions shown in Table <NUM> while applying pressurizing force in the vertical direction to form an ultrasonic joint part integrated by ultrasonic joining. A corrosion test was conducted on each of the ultrasonic joint part thus obtained, electric resistance and pull-out strength were measured before and after the corrosion test, an increasing ratio of electric resistance and a decreasing ratio of pull-out strength after the corrosion test were calculated, and corrosion resistance was comprehensively evaluated from these calculated values.

A total contacting length L and a summed length of a contour line of a space were measured by a method in which a cross-section of the ultrasonic joint part <NUM> is captured by using an optical microscope or an electron microscope and an extending shape of the joint interface (illustrated by the solid line in <FIG>) can be approximated as much as possible from the captured image or photograph, for example, by a method in which plural straight lines each having a length of <NUM> or less (for example, <NUM>) are used and connected in a line graph as illustrated in <FIG>.

Corrosion tests were conducted by methods of salt spray testing specified in JIS Z2371:<NUM>. Test conditions are as follows.

With respect to a test piece before being subjected to the above corrosion test and a test piece after being subjected to the above corrosion test, the copper-based conductor of the copper-based conductor covered electric wire was attached to one electrode and the aluminum-based conductor of the aluminum-based conductor covered electric wire was attached to another electrode, and electric resistance was measured using a circuit element measuring device manufactured by HIOKI E. CORPORATION (product name: <NUM> AC mΩ HiTESTER) to obtain a ratio (increasing ratio (%)) of the electric resistance of the test piece after the corrosion test increased compared with the electric resistance of the test piece before the corrosion test.

With respect to a test piece before being subjected to the above corrosion test and a test piece after being subjected to the above corrosion test, the ultrasonic joint part and an electric wire part were fixed to a chuck, and pull-out strength was measured. A ratio (decreasing ratio (%)) of the pull-out strength of the test piece after the corrosion test decreased compared with the pull-out strength of the test piece before the corrosion test was obtained.

These evaluation results are shown in Table <NUM>.

Comprehensive evaluation was performed considering the results of the increasing ratio of electric resistance and the decreasing ratio of pull-out strength obtained after the above corrosion test. In comprehensive evaluation, the case where both of the increasing ratio in the electric resistance value and the decreasing ratio of pull-out strength were less than <NUM>% was rated as "good," the case where both of the increasing ratio in the electric resistance value and the decreasing ratio of pull-out strength were less than <NUM>% and at least one thereof was <NUM>% or more was rated as "fair," the case where at least one of the increasing ratio in the electric resistance value and the decreasing ratio of pull-out strength was <NUM>% or more was rated as "poor," and "good" and "fair" were regarded as acceptable levels in the present examples.

From the evaluation results shown in Table <NUM>, each of the electric wire connection structures of Examples <NUM> to <NUM> had an increase ratio of electric resistance suppressed as low as <NUM>% or less, had a decreasing ratio of pull-out strength suppressed as low as <NUM>% or less after the corrosion test, and was excellent in corrosion resistant. On the other hand, the electric connection structures of Comparative Examples <NUM> and <NUM> were imperfectly joined and breakage of the joint part occurred in the electric connection structure of Comparative Example <NUM>, and a sound ultrasonic joint part could not be formed in all of these cases. Further, each of the electric connection structures of Comparative Examples <NUM> and <NUM> had an increasing ratio of electric resistance of <NUM>% or more, had a decreasing ratio of pull-out strength of <NUM>% or more after the corrosion test, and was poor in corrosion resistant.

Claim 1:
An electric wire connection structure (<NUM>) comprising:
one or more copper-based conductor covered electric wires (<NUM>) having a copper-based conductor covered part (<NUM>) in which a copper-based conductor made of copper or a copper alloy is covered with an insulating cover and a copper-based conductor exposed part (<NUM>) in which a part of the insulating cover is stripped by a predetermined length to expose the copper-based conductor; and
one or more aluminum-based conductor covered electric wires (<NUM>) having an aluminum-based conductor covered part (<NUM>) in which an aluminum-based conductor made of aluminum or an aluminum alloy is covered with an insulating cover and an aluminum-based conductor exposed part (<NUM>) in which a part of the insulating cover is stripped by a predetermined length to expose the aluminum-based conductor, wherein
an ultrasonic joint part (<NUM>) is provided at a conductor stacked part in which the copper-based conductor exposed part (<NUM>) and the aluminum-based conductor exposed part (<NUM>) are superposed,
the electric wire connection structure being characterized in that a joint interface of the ultrasonic joint part (<NUM>) satisfies a relational expression of <MAT>
where a total contacting length which is a summed length of a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part contact is L and a summed length of a contour line of a space formed at a part at which the copper-based conductor exposed part and the aluminum-based conductor exposed part are separate is x based on cross-section observation,
the joint interface of the joint part (<NUM>) is provided by the aluminum-based conductor covered electric wire (<NUM>) being the only one plastically deformed or melted in a gap unjoined which is formed between the copper-based conductor exposed part (<NUM>) and the aluminum-based conductor exposed part (<NUM>) forming the joint interface so as to fill the gap of the copper-based conductor covered electric wire (<NUM>) based on cross-section observation wherein a difference in tensile strength between the copper-based conductor and the aluminum-based conductor is <NUM> MPa or more.