Bus bar welding method and bus bar structure

Abstract

The present invention is a method for welding a bus bar (6), the method comprising: a step for preparing the bus bar (6), the bus bar (6) having a first flat surface part (2), a curved part (5), and a second flat surface part (1) in this order in the longitudinal direction; a step for bringing a joint surface (4) of a joined body (3) into contact with the first flat surface part (2) of the bus bar (6); and a step for joining the bus bar (6) and the joined body (3) by subjecting a groove part (7) to laser irradiation for butt welding, the groove part (7) being constituted by the joint surface (4) of the joined body (3) and the curved part (5) of the bus bar (6).

Description

Busbar welding method and busbar structure

[0001] The present invention relates to a method for welding a bus bar.

[0002] For example, in an electric vehicle or the like that uses a motor as a driving force, power is supplied from an inverter to the motor. For this reason, electrical connectors such as an electrical junction box or terminal block are provided to electrically connect the motor and the inverter. Such electrical connectors are provided with bus bars, and power distribution members such as wire harnesses are connected to both ends of the bus bars to form a circuit in the electric vehicle or the like.

[0003] Various studies have been conducted to effectively join bus bars. Patent Document 1 (JP 10-334957 A) discloses a laser-welded bus bar structure in which tab-shaped portions raised from pattern portions of different layers of stacked bus bars are overlapped and the overlapped tab-shaped portions are welded together with a laser beam. Patent Document 2 (JP 11-297380 A) discloses a bus bar structure for an electrical connection box in which a short terminal holding portion is formed on the bus bar, while an upper relay terminal is provided with only a contact portion into which a terminal of an electronic component is inserted, and a press-fit portion that is press-fitted into the terminal holding portion of the bus bar is integrally formed with the relay terminal, and the press-fit portion is press-fitted into the terminal holding portion of the bus bar for joining.

[0004] JP-A No. 10-334957 JP-A No. 11-297380

[0005] In the laser welding structure of Patent Document 1, when the tab-shaped portions of the stacked bus bars are overlapped with each other, the tab-shaped portions must be overlapped with precise positional accuracy. Therefore, if the upper surface of one tab-shaped portion is misaligned with the upper surface of the other tab-shaped portion when the tab-shaped portions of the stacked bus bars are overlapped with each other, it is difficult to sufficiently weld the overlapped tab-shaped portions together. Furthermore, in the laser welding structure of the bus bars of Patent Document 1, if a force acts on the stacked bus bars in a direction that moves them apart, a gap is created between the overlapping portions of the tab-shaped portions, and the laser or electron beam penetrates the gap, making it difficult to weld using a laser or electron beam.

[0006] In the bus bar structure of the electrical junction box of Patent Document 2, the bus bar is welded to the receptacle terminal (relay terminal), which requires space for the receptacle terminal, making it difficult to miniaturize the electrical junction box. Also, the increased number of electrical connection points between the bus bar and the receptacle terminal causes problems such as heat generation and reduced reliability.

[0007] The present invention has been made in view of the above-mentioned problems, and has an object to provide a bus bar welding method that can effectively weld a bus bar to an object to be joined.

[0008] A busbar welding method according to the present invention includes the steps of: preparing a busbar having a first flat portion, a curved portion, and a second flat portion in this order along the longitudinal direction; bringing a joining surface of a workpiece into contact with the first flat portion of the busbar; and irradiating a laser beam onto a groove formed by the joining surface of the workpiece and the curved portion of the busbar, thereby performing butt welding and joining the busbar and the workpiece.

[0009] According to the busbar welding method of the present invention, groove welding is possible by irradiating a laser beam onto a groove defined by the joining surface of the workpiece and the curved portion of the busbar to perform butt welding. Therefore, compared to welding performed on overlapping tab-shaped portions of the busbar, as in Patent Document 1, stable welding quality and welding area can be obtained. Furthermore, because the contact area between the joining surface of the workpiece and the first flat portion is large, when butt welding is performed by irradiating a laser beam onto the groove, it is possible to prevent the laser from passing through the workpiece and the busbar and damaging surrounding components, and to prevent material from scattering around the workpiece and the busbar. As a result, the busbar can be effectively welded to the workpiece. The "longitudinal direction" refers to the direction perpendicular to the thickness and width directions of the busbar.

[0010] In one embodiment of the present invention, in the step of bringing the joining surfaces of the workpieces into contact with the first flat portion of the busbar, the joining surfaces of the workpieces may be brought into contact with the first flat portion of the busbar by pressing the second flat portion toward the workpieces in the longitudinal direction of the second flat portion. With this configuration, the force applied by pressing the second flat portion is more likely to be effectively transmitted to the contact area between the joining surfaces of the workpieces and the first flat portion due to deformation of the curved portion of the busbar. As a result, the joining surfaces of the workpieces and the first flat portion can be placed in a sufficiently parallel positional relationship, thereby effectively bringing the joining surfaces of the workpieces into contact with the first flat portion.

[0011] In one aspect of the present invention, the step of preparing a busbar may include preparing a busbar in which the angle between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion is greater than 90° and less than 110°. With this configuration, the angle between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion is greater than 90° and less than 110°, i.e., an obtuse angle slightly greater than 90°. Therefore, the force applied to the second flat portion in the step of bringing the joining surfaces of the workpieces into contact with the first flat portion of the busbar can be more effectively transmitted to the contact area between the joining surfaces of the workpieces and the first flat portion due to deformation of the curved portion of the busbar. Furthermore, typically, after deformation of the curved portion of the busbar, the angle between the longitudinal direction of the first flat portion of the busbar and the longitudinal direction of the second flat portion of the busbar is approximately 90°. As a result, the joining surface of the object to be joined and the first flat portion can be fixed in contact with each other without any gaps, and welding can be performed reliably without the laser or electron beam penetrating through.

[0012] In one embodiment of the present invention, the object to be joined may be a terminal portion of an automobile part. Many parts are used in an automobile, and many electrical connections are made. According to this configuration, since the object to be joined is an automobile part, an excellent electrical connection can be formed between the automobile part and the bus bar. Furthermore, since there is no need to provide a receptacle terminal for the electrical connection of the bus bar, the electrical connection body including the bus bar can be made smaller, allowing for effective space to be provided for other components inside the automobile. When the object to be joined is an automobile part, the joining surface can be the surface of a terminal portion protruding from the part. Furthermore, the automobile is not particularly limited, and examples thereof include automobiles driven by internal combustion engines and electric vehicles.

[0013] In one configuration of the present invention, the automotive component may be selected from a relay, a resistor, a fuse, and a current sensor. According to this configuration, by welding the busbar to a joining surface of a component selected from the relay, resistor, fuse, and current sensor, which is a joined object, an excellent electrical connection can be formed between the joined object and the busbar. The busbar structure of the present invention includes: a busbar having a flat portion and a curved portion; a joined object having a plate-shaped portion; and a groove formed from the plate-shaped portion to the curved portion by abutting the flat portion of the busbar against the plate-shaped portion of the joined object. According to this busbar structure, groove welding is possible by irradiating a laser onto the groove portion to perform butt welding. Therefore, compared to welding at overlapping portions of the tab-shaped portions of the busbar as in Patent Document 1, stable welding quality and welding area can be obtained. Furthermore, because the contact area between the plate-like portion of the workpiece and the flat portion of the busbar is large, when a laser is irradiated into the groove to perform butt welding, the laser can be prevented from passing through the workpiece and the busbar and damaging surrounding components, and the material of the workpiece and the busbar can be prevented from scattering into the surrounding area, thereby enabling the busbar to be effectively welded to the workpiece.

[0014] A bus bar welding method can be provided that can effectively weld a bus bar to an object to be joined.

[0015] FIG. 1 is a diagram illustrating a busbar welding method according to one embodiment.

[0016] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram illustrating a busbar welding method according to this embodiment. More specifically, Fig. 1(a) is a perspective view illustrating a step of bringing the joining surfaces of the workpieces into contact with a first flat portion of the busbar, and a step of irradiating a laser onto the groove portion to perform butt welding to join the busbar and the workpieces. Fig. 1(b) is a cross-sectional view taken along the line AA' in Fig. 1(a).

[0017] FIG. 1 shows a portion where a busbar 6 and a workpiece 3 are joined. An actual busbar extends in the upper right direction of the drawing, and the busbar 6 in FIG. 1 shows the terminal portion of the busbar to be joined to the workpiece 3. The workpiece 3 is a terminal portion of a component mounted on an automobile, and the body of the component is connected to the workpiece 3 in FIG. 1 . FIG. 1 shows a busbar structure. This busbar structure includes a busbar 6 having a flat portion (first flat portion 2) and a curved portion 5, a workpiece 3 having a plate-shaped portion (the joining surface 4 indicates the plane where the plate-shaped portion abuts against the first flat portion 2), and a groove portion 7 formed from the plate-shaped portion to the curved portion 5 by the flat portion (first flat portion 2) of the busbar 6 abutting against the plate-shaped portion of the workpiece 3. In the busbar welding method of this embodiment, first, a busbar 6 having a first flat portion 2, a curved portion 5, and a second flat portion 1 in this order along a longitudinal direction D5 is prepared. As shown in FIGS. 1A and 1B , the longitudinal direction D5 represents a direction perpendicular to the thickness direction D6 and width direction D7 of the busbar 6 at a specific position in the longitudinal direction D5. As shown in FIG. 1 , the busbar 6 is formed by integrating a first planar portion 2, a curved portion 5, and a second planar portion 1. The first planar portion 2 is a plate-like portion having two opposing surfaces, and the second planar portion 1 is a plate-like portion having two opposing surfaces. The curved portion 5 has a curved shape with a predetermined curvature, and one end of the curved portion 5 in the longitudinal direction D5 is connected to the first planar portion 2, and the other end of the curved portion 5 in the longitudinal direction D5 is connected to the second planar portion 1. The first planar portion 2, the curved portion 5, and the second planar portion 1 are positioned continuously along the longitudinal direction D5 to form the terminal portion of the busbar 6. At this time, the longitudinal direction D4 of the first planar portion 2 and the longitudinal direction D3 of the second planar portion 1 are parallel to the longitudinal direction D5.

[0018] In the prepared busbar 6, the angle D4 between the longitudinal direction D3 of the second flat portion 1 and the longitudinal direction D4 of the first flat portion 2 can be in the range of greater than 90° and not greater than 110°. By setting the angle to be in the range of greater than 90° and not greater than 110°, i.e., an obtuse angle slightly greater than 90°, the force applied to the second flat portion 1 in the direction D2 in the step of bringing the joining surface 4 of the workpiece 3 into contact with the first flat portion 2 of the busbar 6 can be more effectively transmitted to the contact area between the joining surface 4 of the workpiece 3 and the first flat portion 2 due to deformation of the curved portion 5 of the busbar 6. Furthermore, as shown in FIG. 1( b ), the angle between the longitudinal direction D4 of the first flat portion 2 of the busbar 6 and the longitudinal direction D3 of the second flat portion 1 of the busbar 6 after deformation of the curved portion 5 of the busbar 6 is typically approximately 90°. As a result, the joining surface 4 of the workpiece 3 and the first flat portion 2 can be fixed in contact with each other without any gaps, allowing for reliable welding without penetration of the laser or electron beam. The "angle between the longitudinal direction of the first flat portion of the busbar and the longitudinal direction of the second flat portion of the busbar" refers to the angle at the intersection of the longitudinal direction D4 of the first flat portion and the longitudinal direction D3 of the second flat portion, as shown in FIG. 1( b). The "angle between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion" can be changed by deforming the curved portion 5. For example, the "angle between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion" in the step of bringing the joining surface of the workpiece 3 into contact with the first flat portion of the busbar is smaller than the "angle between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion" in the busbar prepared in the step of preparing the busbar. Typically, the "angle formed between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion" after welding is 90°.

[0019] Next, the joining surface 4 of the object 3 is brought into contact with the first flat portion 2 of the busbar 6. More specifically, as shown in FIGS. 1( a) and 1(b), the second flat portion 1 is pressed toward the object 3 in the longitudinal direction D3 of the second flat portion 1 in the direction D2 toward the object 3, thereby bringing the joining surface 4 of the object 3 into contact with the first flat portion 2 of the busbar 6. At this time, the force applied by pressing the second flat portion 1 is easily transmitted effectively to the contact portion between the joining surface 4 of the object 3 and the first flat portion 2 due to the deformation of the curved portion 5 of the busbar 6. As a result, the joining surface 4 of the object 3 and the first flat portion 2 can be placed in a sufficiently parallel positional relationship, thereby bringing the joining surface 4 of the object 3 into effective contact with the first flat portion 2. The object 3 is, for example, a terminal portion of an automobile part, and the automobile part is selected from a relay, a resistor, a fuse, and a current sensor. When the object 3 is an automobile part, the joining surface 4 can be a terminal portion protruding from the automobile part. When the angle between the longitudinal direction D4 of the first flat portion 2 and the longitudinal direction D3 of the second flat portion 1 in the busbar 6 before contact with the joining surface 4 of the object 3 is greater than 90°, the curved portion 5 is deformed by the force applied by pressing the second flat portion 1. As a result, the angle between the longitudinal direction D4 of the first flat portion 2 and the longitudinal direction D3 of the second flat portion 1 in the busbar 6 after contact with the joining surface 4 becomes smaller than the angle between the longitudinal direction D4 of the first flat portion 2 and the longitudinal direction D3 of the second flat portion 1 in the busbar 6 before contact with the joining surface 4. Typically, as shown in FIG. 1( b ), the angle between the longitudinal direction D4 of the first flat portion 2 and the longitudinal direction D3 of the second flat portion 1 after contact with the joining surface 4 is 90°. 1(b), the joining surface 4 of the workpiece 3 and the first flat portion 2 of the bus bar 6 come into contact with each other, thereby forming a groove portion 7 constituted by the curved portion 5 and the workpiece 3. The groove portion 7 becomes a groove when butt welding, which will be described later, is performed.

[0020] 1(a), a laser is irradiated from the direction D4 onto the groove 7 formed by the joining surface 4 of the workpiece 3 and the curved portion 5 of the bus bar 6, and the laser is scanned in the direction D1 to perform butt welding, melting the materials forming the workpiece 3 and the curved portion 5, thereby joining the bus bar 6 and the workpiece 3. The workpiece 3 and the bus bar 6 may be plated. Because plating has low laser reflectivity and easily absorbs the laser, the workpiece 3 and the curved portion 5 can be melted with a low laser output.

[0021] According to this embodiment, the curved portion 5 is easily deformed due to its curvature, and even if there is a dimensional error in the objects to be joined 3 and the first flat portion 2, the deformation of the curved portion 5 allows the first flat portion 2 to be in good contact with the objects to be joined 3. As a result, the first flat portion 2 of the busbar 6 can be brought into contact with the joining surface 4 so that no gap is generated between the first flat portion 2 and the joining surface 4 of the objects to be joined 3. In other words, even if the joining surface 4 and the first flat portion 2 are not parallel when the first flat portion 2 is brought into contact with the joining surface 4 of the objects to be joined 3, the deformation of the curved portion 5 corrects the positional relationship between the joining surface 4 of the objects to be joined 3 and the first flat portion 2, and the joining surface 4 and the first flat portion 2 can finally be brought into contact so that the joining surface 4 and the first flat portion 2 are parallel.

[0022] According to this embodiment, butt welding is performed by irradiating a laser onto the groove portion 7 formed by the joining surface 4 of the workpiece 3 and the curved portion 5 of the busbar 6. This allows for stable welding quality and a stable welding area between the joining surface 4 of the workpiece 3 and the first flat portion 2, compared to welding performed on overlapping portions of the tab-shaped portions of the busbar as in Patent Document 1. Furthermore, because the contact area between the joining surface 4 of the workpiece 3 and the first flat portion 2 is large, when butt welding is performed by irradiating a laser onto the groove portion 7, it is possible to prevent the laser from passing through the workpiece 3 and the busbar 6 and damaging surrounding components, or to prevent materials from scattering around the workpiece 3 and the busbar 6. Furthermore, when electrically connecting the second flat portion 1 of the busbar 6 to a component, power source, or the like, an external force acts on the second flat portion 1 toward the workpiece 3 in the longitudinal direction D3. This presses the first flat portion 2 against the joining surface 4 of the workpiece 3, making it difficult for the first flat portion 2 to separate from the joining surface 4 of the workpiece 3. Furthermore, since receptacle terminals are no longer necessary, the electrical connection assembly including the bus bar 6 can be made smaller. In the above embodiment, the positional relationship between the workpiece 3, which is the terminal portion of the component, and the main body of the component is not specified. However, it is preferable that the main body of the component is not disposed in a direction extending from the longitudinal direction D5 toward the first flat surface portion 2. By disposing the workpiece 3 and the main body of the component in this manner, a gap is created between the joining surface 4 of the workpiece 3 and the first flat surface portion 2 of the bus bar 6. This prevents damage to the main body of the component even if the laser passes through the gap between the workpiece 3 and the bus bar 6. Furthermore, scattering of spatter onto the main body during laser irradiation can be suppressed.

[0023] REFERENCE SIGNS LIST 1 Second flat portion 2 First flat portion 3 Joined body 4 Joining surface 5 Curved portion 6 Bus bar 7 Groove portion

Claims

1. A busbar welding method comprising the steps of: preparing a busbar having a first flat portion, a curved portion, and a second flat portion in that order along the longitudinal direction; bringing the joining surfaces of the objects to be joined into contact with the first flat portion of the busbar; and irradiating a laser beam onto a groove formed by the joining surfaces of the objects to be joined and the curved portion of the busbar to perform butt welding, thereby joining the busbar and the objects to be joined.

2. The busbar welding method according to claim 1, wherein in the step of bringing the joining surfaces of the workpieces into contact with the first flat portion of the busbar, the joining surfaces of the workpieces are brought into contact with the first flat portion of the busbar by pressing the second flat portion toward the workpieces in the longitudinal direction of the second flat portion.

3. The busbar welding method according to claim 2, wherein in the step of preparing the busbar, an angle formed between the longitudinal direction of the first flat portion and the longitudinal direction of the second flat portion is in the range of more than 90° and not more than 110°.

4. The busbar welding method according to claim 1 or 2, wherein the object to be joined is a terminal portion of an automobile part.

5. The busbar welding method according to claim 4, wherein the automotive component is selected from the group consisting of a relay, a resistor, a fuse, and a current sensor.

6. A busbar structure comprising: a busbar having a flat portion and a curved portion; a joined body having a plate-like portion; and a groove portion formed from the plate-like portion to the curved portion by the flat portion of the busbar abutting against the plate-like portion of the joined body.

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