Thermal method for materially joining two busbars at low thermal load

Abstract

The invention relates to a thermal method for materially joining two busbars (1, 2) for a motor vehicle, having the following steps: arranging at least two busbars (1, 2) and a hard-soldering plate (3) such that the hard-soldering plate (3) is clamped in a stack between the busbars (1, 2) overlapping the joining regions (1a, 2a) respectively and the hard-soldering plate (3) abutting the respective joining region (1a, 2a) of the associated busbar (1, 2) with the respective joining face (1b, 2b) of the hard-soldering plate (3) facing towards it, and at least one of the joining faces (1b, 2b) forming one or more protrusions (1c); and subsequently materially joining the joining regions (1a, 2a) by heating the joining regions (1a, 1b) and the hard-soldering plate (3), preferably with at least partial melting of the hard-soldering plate (3).

Description

Technical Field

[0001] This invention relates to a thermal method for material locking together two busbars. Background Technology

[0002] In electric vehicles, charging or driving energy is transmitted via busbars. Busbars are solid strips formed from a metallic material with good electrical conductivity. They provide a relatively large conductive cross-section to achieve low power loss. This is especially important when charging the vehicle's battery, where charging power is constantly increasing to rapidly raise the battery's state of charge. Busbars are typically made of copper, aluminum, or a combination thereof. The advantages of copper busbars are that they require a smaller cross-section for the same resistance, thus requiring less construction space, and have lower transition resistance in the contact area compared to aluminum busbars. The disadvantage of aluminum in the contact area is its susceptibility to corrosion and the poor conductivity of the corrosion layer. Therefore, aluminum busbars are generally coated in the contact area. Compared to copper busbars, aluminum busbars offer advantages such as approximately half the weight and lower cost for the same resistance. However, aluminum busbars require a larger cross-section and thus greater construction space. Busbars are partially connected to each other by clamping or screw connections for force locking. These connections do not save weight and therefore it is preferable to interlock and weld the busbars together. Welding busbars, especially in processes such as arc welding or resistance welding, presents a number of disadvantages and risks due to the high temperatures: high temperatures can cause changes in the crystal structure of the material, leading to a reduction in strength or toughness in the weld zone. This can affect the service life of the busbar and cause premature wear or breakage. Due to uneven heat distribution during welding, especially due to large temperature gradients, the busbar may twist or deform, affecting fit accuracy and function. Different cooling rates in the weld zone can cause temperature-induced internal stresses in the material. These stresses can eventually lead to tearing or fracture, especially under repeated loads.

[0003] When welding is applied to busbars already housed in a housing shared with electronic components, it can also create significant disadvantages for nearby electronic components, primarily due to heat generation and the resulting electromagnetic effects. The most critical risks include thermal damage, thermal strain, electromagnetic interference (EMI), current spikes, and overvoltage. In some cases, welding can also lead to increased ambient temperatures, making nearby components susceptible to corrosion or oxidation, especially if they are not adequately protected against high temperatures. Summary of the Invention

[0004] Therefore, the fundamental object of the present invention is to provide a thermal method for material-lockingly connecting two busbars, wherein the thermal load on the environment, and especially on the two mating components (i.e., the two busbars), is reduced. This object is achieved by the features of the independent claim. Advantageous improvements of the invention are derived from the dependent claims.

[0005] This invention relates to a thermal method for locking two busbar materials for a motor vehicle, the thermal method comprising the following steps: In the arrangement step, at least two buses and solder plates are arranged such that the solder plates are stacked and clamped between the buses overlapping the joints, with the solder plates abutting the respective joints of the associated buses, facing the joint surfaces of the solder plates. At least one of the joint surfaces forms one or more protrusions, preferably arranged within and spaced apart from the outer periphery of the joint surface, more preferably arranged in the center. The protrusions are, for example, single, bead-like protrusions located in the flat area of ​​the joint surface, appearing bead-like in a top view of the joint surface. The protrusions have a height of, for example, 0.2 mm to 0.8 mm, preferably 0.3 mm to 0.6 mm, relative to the rest of the surrounding area of ​​the joint surface. The joints of at least the buses are formed, for example, substantially plate-like, with rectangular cross-sections and two opposing main surfaces. One of the main surfaces of the joint forms the joint surface, for example. The buses are formed, for example, substantially of a metal alloy, of a metal (such as aluminum or copper). The joints may have a thin metal coating. The busbar is used, for example, to guide the charging and discharging current of the power battery of an electrically driven motor vehicle. In a subsequent step of the method according to the invention, the joint material is locked together by heating the joint and the solder plate. Preferably, the heating is performed by partially melting the solder plate, and more preferably by completely melting the solder plate.

[0006] Preferably, in order to at least partially melt the solder plate, a voltage is applied to the busbar, causing current to flow through a dotted contact area formed by the at least one protrusion and generating localized resistance heating in the contact area, wherein melting of the solder plate begins in the dotted contact area and subsequently spreads across the solder plate. The heating is preferably achieved solely by applying voltage.

[0007] More preferably, the solder plates are initially arranged such that the only point-like contact area formed by the protrusions (i.e., the contact area formed only by the protrusions) is formed between the corresponding mating surface and the solder plate, while the remaining area of ​​the corresponding mating surface is spaced apart from the solder plate, for example, via an air gap. Thus, in the initial stage, this arrangement has a relatively high transition resistance. If a voltage is applied to the two buses in a subsequent step, a larger current flows through the only point-like contact area and causes localized heating (resistive heating) due to the increased transition resistance. Due to this localized heating, the solder plate first melts within the area of ​​the only contact area, where the liquid brazing region then extends from the contact area onto the solder plate, thereby creating a material-locked connection across the entire mating surface. This advantageously achieves targeted, localized heat input, thereby reducing the thermal load on the bus and adjacent components.

[0008] In most cases, heating is preferably performed such that it does not exceed the liquidus temperature, preferably the solidus temperature, of the busbar material (especially copper) and exceeds the liquidus temperature of the solder plate, i.e., the joint is brazed, for example, according to the general definition of "löten". For example, the joint and the solder plate are heated to a temperature in the range of 450.0°C to 1084.0°C.

[0009] Avoiding high temperatures, such as those above the liquidus temperature of copper, eliminates changes in the material's crystal structure, thus preserving the original strength or toughness of the bus. This maintains the bus's lifespan and prevents premature wear or breakage. The hard solder plate achieves a more uniform heat distribution, preventing the bus from twisting or deforming without affecting fit accuracy and functionality. With reduced heat load, electronic components housed in the same housing as the bus experience less heat. This reduces adverse side effects such as thermal stress, electromagnetic interference (EMI), current spikes, overvoltage, corrosion, or oxidation.

[0010] The non-protruding mating surfaces of these two busbars are preferably formed to be flat.

[0011] Preferably, the method includes an imprinting step prior to the arrangement, wherein the junction of at least one busbar is imprinted to form the at least one protrusion.

[0012] Preferably, the step of welding or brazing the at least one protrusion to the junction of at least one busbar is performed in time prior to the arrangement step and possibly after the imprinting step.

[0013] The solder plate is preferably formed from a phosphorus-containing low-melting-point solder, which preferably contains 15% by weight of silver, 80% by weight of copper and 5% by weight of phosphorus.

[0014] Preferably, at least one busbar and / or the solder plate has positioning components for easy arrangement.

[0015] Preferably, in the arrangement, the solder plate extends from at least one of the stacked buses to form a lateral contact surface relative to the stacking direction on the end face or side face of at least one of the buses as a positioning element. For example, the solder plate has a folded edge for aligning and placing the solder plate onto one of the buses.

[0016] Preferably, the solder plate and one of the busbars form a locating component that cooperates in force-locking and / or form-locking. For example, the solder plate has a through hole that is engaged by a locating pin of one of the busbars in the arrangement. Preferably, a tongue, such as an element of a sheet nut, is arranged extending radially inward into the through hole, by means of which the solder plate can be quickly and tool-free installed or arranged and secured against loosening by the synergistic force-locking action. The locating pin can be produced, for example, by pressure forming of the busbar and is located outside the mating surface of the respective busbar in the two buses.

[0017] Preferably, the solder plate has a lateral protrusion on both mating surfaces relative to the stacking direction, and the positioning component (such as the through hole) of the solder plate is formed in the protrusion. Attached Figure Description

[0018] The present invention will now be explained in detail with reference to the following accompanying drawings and embodiments. In the drawings: Figure 1 An exploded three-dimensional view is shown to illustrate an embodiment of the thermal method for locking two busbar materials together according to the present invention; Figure 2 Showing relevant detailed images; Figure 3 A relevant three-dimensional cross-sectional view is shown after the arrangement steps of the thermal method according to the invention; Figure 4 A top view of the solder plate 3 used in the thermal method according to the present invention is shown; Figure 5 A cross-sectional view of the solder plate 3 used in the thermal method according to the present invention is shown. Detailed Implementation

[0019] This invention relates to a thermal method for locking two busbar materials for a motor vehicle, the thermal method comprising the following steps: In the Figure 1 and Figure 2 In the arrangement steps derived from the exploded view, at least two busbars 1 and 2 and a solder plate 3 are arranged such that the solder plate 2 is stacked and sandwiched between busbars 1 and 2 that overlap with joints 1a and 2a respectively, and the solder plate 3 is adjacent to the respective joint surfaces 1b and 2b of the respective joints 1a and 2a of the associated busbars 1 and 2 facing the solder plate 3. The solder plate 3 is formed, for example, of a phosphorus-containing low-melting-point solder, which preferably has 15% by weight of silver, 80% by weight of copper, and 5% by weight of phosphorus.

[0020] At least one of the two mating surfaces 1b and 2b (here, mating surface 1b) forms a central protrusion 1c, wherein the protrusion 1c is arranged within the outer periphery of mating surface 1b, more precisely, at the geometric midpoint of mating surface 1b and thus in the center. The protrusion 1c is a single, bead-like protrusion located in the flat area of ​​mating surface 1b, as seen in a top view of mating surface 1b. The protrusion 1c has a height of 0.2 mm to 0.8 mm, preferably 0.3 mm to 0.6 mm, relative to the rest of the surrounding area of ​​mating surface 1b. The mating surface 2b of the other busbar 2 is formed to be flat and without protrusions.

[0021] For example, in the earlier imprinting step, the protrusion 1c is imprinted into the joint 1a of the busbar 1 and / or the at least one protrusion 1c is welded or brazed to the joint 1a of the busbar 1 as a "solder bead". In the arrangement step, the solder plate 3 is first arranged such that the only point-like contact area formed by the protrusion 1c (that is, the contact area formed only by the protrusion) is formed between the corresponding joint surface 1b and the solder plate 3, while the remaining area of ​​the corresponding joint surface 1b is spaced apart from the solder plate 3 by an air gap.

[0022] like Figure 1 and Figure 2 As shown, at least the joints 1a and 2a of busbars 1 and 2 are formed in a substantially plate-like shape, wherein these joints form a rectangular cross-section and two opposing main surfaces. One of the main surfaces of joints 1a and 2a forms joint surfaces 1b and 2b, respectively.

[0023] The joints 1a and 2a have a thickness of 1 mm to 4 mm perpendicular to the joint surfaces 1b and 2b, and a width of, for example, 7 mm to 20 mm, thus making them suitable for high-voltage applications and corresponding power transmission. Buses 1 and 2 are used, for example, to guide the charging and discharging current of a power battery in an electrically driven motor vehicle. Buses 1 and 2 are formed, for example, substantially of a metal alloy (such as a copper-containing alloy) or of a metal (such as aluminum or copper). The joints 1a and 2a may have a thin metal coating, such as a gold coating. Preferably, the method includes an imprinting step prior to the arrangement, wherein the joint of at least one bus is imprinted to form the at least one protrusion. Figure 2 and Figure 3 As shown, in the arrangement, the solder plate 3 extends from busbar 1 in the stacked busbars 1 and 2, so as to form a lateral contact surface on the end face or side face of busbar 1 relative to the stacking direction as a positioning component. More specifically, the solder plate 3 has a... Figure 4 and Figure 5 The fold 3a shown in detail is used to align the solder plate 3 with the busbar 1 and place it thereon.

[0024] like Figure 2 and Figure 4 As shown, the solder plate 3 and the busbar 1 form a positioning component that cooperates in a force-locking and form-locking manner. The solder plate 3 thus has a through hole 3b, which is engaged by the positioning pin 1d of the busbar 1 during arrangement. Here, in the through hole 3b of the solder plate 3, like an element of a sheet nut, tongues 3c are arranged radially from the outside to the inside, allowing the solder plate 3 to be quickly and tool-free installed or arranged, and secured against loosening through the force-locking cooperation. The positioning pin 1d can be produced, for example, by pressure forming of the busbar 1 and is located outside the mating surface 1b of the busbar 1.

[0025] In a subsequent step of the method according to the invention, the joint materials of the joints 1a, 2a and the solder plate 3 are locked together by heating. Here, heating is performed when the solder plate 3 is partially melted, and more preferably when the solder plate 3 is completely melted. Here, in order to at least partially melt the solder plate, a voltage is applied to the busbars 1, 2, such that current flows through the point-like contact area formed by the protrusion 1c and local resistance heating is generated in the contact area, wherein the melting of the solder plate 3 begins in the point-like contact area and then spreads on the solder plate 3. Here, heating is performed solely by applying a voltage.

[0026] In most cases, heating is preferably performed such that it does not exceed the liquidus temperature, preferably the solidus temperature, of the busbar material (especially copper) and exceeds the liquidus temperature of the solder plate, i.e., the joint is brazed, for example, according to the general definition of "brazing". For example, the joints 1a, 2a and the solder plate 3 are heated to a temperature in the range of 450.0°C to 1084.0°C.

[0027] Avoiding high heat, such as temperatures above the liquidus of copper, eliminates changes in the material's crystal structure, thus preserving the original strength or toughness of buses 1 and 2. This maintains the service life of buses 1 and 2 and prevents premature wear or breakage. The solder plate 3 achieves a more uniform heat distribution, preventing bus distortion or deformation without affecting fit accuracy and functionality. With reduced heat load, electronic components housed in the shared housing with buses 1 and 2 experience less heat load. This reduces adverse side effects such as thermal strain, electromagnetic interference (EMI), current spikes, overvoltage, corrosion, or oxidation.

Claims

1. A thermal method for locking two busbars (1, 2) for use in a motor vehicle, said thermal method comprising the following steps: At least two busbars (1, 2) and solder plates (3) are arranged such that the solder plates (3) are stacked and clamped between the busbars (1, 2) that overlap with the joints (1a, 2a) respectively, and the solder plates (3) are respectively adjacent to the respective joints (1a, 2a) of the associated busbars (1, 2) with their respective joint surfaces (1b, 2b) facing the solder plates (3), and at least one of the joint surfaces (1b, 2b) forms one or more protrusions (1c). The joints (1a, 2a) are then locked together by heating the joints (1a, 1b) and the solder plate (3), preferably by at least partially melting the solder plate (3).

2. The thermal method according to claim 1, wherein in order to at least partially melt the solder plate (3), a voltage is applied to the bus (1, 2) such that current flows through a point-like, preferably only touch contact area formed by the at least one protrusion (1c) and generates local resistance heating in the touch contact area, wherein the melting of the solder plate (3) begins within the range of the point-like touch contact area and subsequently extends on the solder plate (3).

3. The heating method according to any one of the preceding claims, wherein the heating is performed such that it does not exceed the liquidus temperature of the material of the busbar (1, 2), particularly copper, preferably not exceeding its solidus temperature and exceeding the liquidus temperature of the solder plate (3).

4. The thermal method according to any one of the preceding claims, wherein the non-protruding mating surface (2b) of the busbar (1, 2) is formed as flat.

5. The thermal method according to any one of the preceding claims, wherein, in a step prior to the arrangement, the joint (1a) of at least one busbar (1, 2) is embossed to form the at least one protrusion (1c).

6. The thermal method according to any one of the preceding claims, wherein, in a step prior to the arrangement, the at least one protrusion (1c) is welded or brazed to the joint (1a) of at least one busbar (1, 2).

7. The thermal method according to any one of the preceding claims, wherein the solder plate (3) is formed of a phosphorus-containing low-melting-point solder, wherein the solder preferably has 15% by weight of silver, 80% by weight of copper and 5% by weight of phosphorus.

8. The thermal method according to any one of the preceding claims, wherein at least one busbar (1, 2) and / or the solder plate (3) has a positioning element.

9. The thermal method according to the preceding claim, wherein, in the arrangement, the solder plate (3) extends from at least one of the stacked busbars to form a laterally mating surface (3a) relative to the stacking direction on the end face or side face of at least one of the busbars (1, 2) as a positioning member.

10. The thermal method according to any one of the preceding two claims, wherein the solder plate (3) and one of the busbars (1, 2) form a positioning component that cooperates in force locking and / or form locking.

11. The thermal method according to the preceding claim, wherein the positioning member has a positioning pin (1d) and a through hole (3b) for receiving the positioning pin.

12. The thermal method according to the preceding claim, wherein a plurality of radially inwardly projecting tongues (3c) are formed in the through hole (3b).

13. The thermal method according to any one of claims 8 to 11, wherein the solder plate (3) has lateral protrusions on two mating surfaces (1b, 2b) relative to the stacking direction, and the positioning member of the solder plate (3) is formed in the protrusions.

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