The present invention concerns a method for forming a connection between a bus bar and a contact section, a busbar being connected to a contact section and a power distribution system having such busbar.

Laminated busbars typically comprise conductive sections of fabricated copper separated by thin dielectric materials, laminated into a unified structure. Examples for laminated busbars can be found in CN 203 504 394 U, CN 104 022 414 A1 or CN 202 474 475 U. Usually a contact section is included in the busbar, in order to connect electrical poles of an electronic component, such as a capacitor, an IGBT and even another connection busbar, directly to different conductive sections, wherein each of the conductive sections is assigned to a type of poles provided by each component. Typically, the components are connected to the connected re gion by nuts and bolts/pins

Further, it is known, for example from US 5,579,217, to use conductive sections made from aluminum. Thus, a comparable light busbar can be provided. For avoiding corrosion or oxidation of these busbars, the busbar is typically covered by a nickel and/or tin cladding, in particular a nickel and/or tin plating. However, cov ering the whole busbar with a nickel and/o tin plating is comparable cost intensive. Considering the above, it is an object of the present invention to provide a method for manufacturing a busbar and to provide a busbar that is improved compared to those known in the state of the art, in particular with respect to a cost efficiency of the manufacturing process and/or a durability of the manufactured busbar.

This object is achieved by a method to form a connection between a busbar and a contact section according to claim 1 , a busbar being connected to a contact sec tion according to claim 14 a power distribution system having a busbar according to claim 15. Preferred embodiments are incorporated in the dependent claims, the description and the figures.

According to a first aspect of the present invention a method for forming a connec tion between a busbar and a contact section is provided, comprising:

- providing a first conductive section made from aluminum,

- providing a second conductive section made from aluminum, wherein the sec ond conductive section includes the contact section or is connected to the contact section and wherein the second conductive section is at least partially covered with nickel and/or tin and

- creating a bond, in particular a laser welding seam, i. e. a laser welding bond, between the first conductive section and the second conductive section, by laser welding.

In contrast to the state of the art, it is provided according to the present invention to connect the contact section to the first conductive section via a second conduc tive section being covered with nickel and/or tin and to perform the connection be tween the first conductive section and the second conductive section by a laser welding process. It turned out that realizing the connection by laser welding estab lishes a durable and resistant connection between the first conductive element and the second conductive section, in particular if the first conductive section is formed by a bare aluminum sheet and the second conductive section, being covered with nickel and/or tin, is connected directly to this bare aluminum sheet, representing the first conductive section. In particular, it turned out to be of advance to use a separate second conductive section for connecting the contact section to the first conductive section, since covering the second conductive section by nickel and/or tin can be performed in a simplified way. Furthermore, the laser welding seam can be realized in a section, being spaced from the contact section, and therefore sim plifies the access of a laser-beam to an interface region between the first conduc tive section and the second conducive section, the laser welding seam preferably extending at least partially along the interface region between the first and the sec ond section in a finished state of the realized connection. As a consequence, a quality of the realized connection can be improved.

In general, it is advantageously possible to realize the nickel and/or tin cover only for the second conductive section and to avoid a covering of the first conductive section with nickel and/or tin. In other words: the durable and resistant connection realized by the laser welding allows restricting the cover only to the first conductive section and it is no longer necessary to cover the whole busbar. Thus, material, namely nickel and/or tin, can be saved and consequently the costs can be re duced, without effecting the durability of the manufactured busbar.

In particular, the contact section is defined as a section being intended to make an electrical contact available, in particular an external contact. In other words: the contacts section represents a terminal to provide the current being conducted by the busbar. For example, the contact section is configured to receive a pin or to connect a cable to the busbar to transfer an electrical current from the busbar. Fur thermore, the second conductive section is preferably a part of the busbar, in par ticular the section without the contact section. Essentially, the first conductive sec tion and the second conductive section form together the busbar and preferably the second conductive section continues the general course of the first conductive section in a main extension plane.

Preferably, the busbar is either a flat product extending in a main extension plane or is bended as a 3D structure, for example U-shaped or L-shaped. The first con ductive section and/or the second conductive section are preferably an aluminum sheet, especially a bare aluminum sheet that mainly defines the main extension plane. For example, the contact section includes a connector element being a bushing for receiving a pin of the electrical component. Preferably, the bushing has an opening for receiving a pin of the electronical component. Thus, for mount ing the electronical component the pin can be inserted into the bushing, in particu lar in the hole of the bushing.

Preferably, the busbar is a flat product extending in a main extension plane. The term “flat” means that a thickness of the busbar, measured in a direction perpen dicular to the main extension plane, is at least 10 times, preferably at least 15 times, smaller than the extensions across the busbar in a plane parallel to the main extension plane. For instance, the busbar is laminated and/or covered with an insulation layer. Such busbars are particularly intended for collecting and trans ferring electrical power. For example, a plurality of capacitors is arranged on top of the busbar and are connected to the busbar for distributing a total power collected from a plurality of capacitors. Such busbars are intended for being used in electri cal vehicles, for example. In particular, the thickness of the busbar, measured in a direction perpendicular to the main extension plane, is between 0.5 mm and 6 mm, more preferably between 3 mm and 6 mm and most preferably between 4.5 mm and 5.5 mm. Although the busbar is comparable thick, it is still configured to be bended to adapt its shape for the corresponding application. In particular, the term “flat” concerns a main body of the busbar, for example at least 70 %, preferably at least 80 % and at least 90 % of the busbar extends in a flat manner. In addition to the pure flat regions or sections, the busbar can include sections extending per pendicular or slanted to a main extension plane of the busbar, thereby being U- shaped for example or L-shaped.

Preferably, the second conductive section has a non-sym metrical cross section in the main extensions plane. The non-symmetrical cross section establishes prefer ably a positive locking with the first conductive section, the positive locking hinder ing the second conductive section from being rotated about an axis perpendicular to the main extension plane. Especially, the second conductive section is not com pletely rotationally symmetric. For example, the second conductive section has a star like, a rectangular or an elliptical shape. Preferably, the cross section is non circular. In particular, the second conductive section is formed such that connect ing the second conductive section with the first connection section makes an ori entation of the second conductive section necessary. Especially, the first conduc tive section and the second conductive section establish a key lock principle.

Thus, it is possible to connect the first conductive section and the second conduc tive section prior to realizing the welding seam.

Preferably, the first conductive layer and the second conductive layer are con nected by a frictional connection, in particular prior to establishing the welding seam. As a consequence, it is possible to connect the first conductive section and the second conductive section in a firm manner, for example for handling the as sembly of the first conductive section and the second conductive section prior to the welding process. As a result, the assembly can be transferred to the welding machine without risking a separation of the first and the second conductive sec tion. Preferably, the first conductive section and the second conductive section es tablishes a press fit.

According to another embodiment of the present invention, the welding seam along the interface section between the first conductive section and the second conductive section is interrupted or extends without an interruption.

Further, it is provided that the connector element is connected to the second con ductive section such that the connector element protrudes from the second con ductive section along a direction being perpendicular to the main extension plane. Especially, the connector element has a front side that faces away from the sec ond conductive section and forms at least a part of a connection surface to which the electronical component, such as a capacitor, an IGBT, or a cable is connected. Preferably, a distance between the second conductive section and said front side facing away from the second conductive section is greater than a thickness of the first conductive section, preferably 1.2 to 5 times, more preferably 1.5 and 4 times and most preferably 2 and 3.5 times greater than the thickness of the first conduc tive section or second conductive section. Said distance and said thickness are measured along the direction perpendicular to the main extension plane. Prefera bly, the first conductive section and/or the second conductive section is covered with an isolation layer. In particular, it is provided that the connector element is covered by nickel and/or tin to realize a low contact resistance on the connector el ement of the contact section, in particular on a connector surface of the connector element.

According to a preferred embodiment the first conductive section and/or the sec ond conductive section comprises several metal sheets being stacked above each other along a stacking direction extending perpendicular to the main extension plane. Preferably, the metal sheets, being stacked above each other, are isolated from each other by an isolation layer, being arranged between at least two of the several metal sheets. For example, the metal sheets have a thickness between 0.5 mm and 5 mm, preferably between 0.75 mm and 2 mm and more preferably between 1 mm and 1.5 mm, in particular measured along the stacking direction. In particular, a height of the connector element is at least 2 to 5 times, more prefera bly 1.5 and 4 times and most preferably 2 and 3.5 times greater than the thickness of the first conductive section, in particular measured along the stacking direction.

Preferably, it is provided that the connector element is made from aluminum. Thus, the weight of the busbar can further decreased. In particular, the reduction of the weight is increased for such busbars having bushings as connector elements pro truding from the top side of the busbar, wherein the bushing is made from alumi num, too. Alternatively, it is also conceivable to use a material different from alu minium for the connector element. In particular, it is provided that the connector el ement and the second conductive section are covered with tin and/or nickel, simul taneously, preferably as combined component. Furthermore, the first conductive section and the second conductive section are preferably formed by flat bodies, extending in a main extension plane, and wherein the first conductive section and the second conductive section are arranged in a common plane, being parallel to the main extension plane. In particular, it is pro vided that the second conductive section continues the general course of the first conductive section in a direction parallel to the main extension plane. Especially, a surface of the first conductive section is flush with a surface of the second conduc tive section, the surfaces being arranged in the same plane. As a consequence, the second conductive section represents a part of the busbar.

Moreover, it is provided that the second conductive section is smaller than the first conductive section. Preferably, an extension of the first conductive section in a di rection parallel to the main extension plane is more than 5 times, preferably more than 10 times and most preferably more than 15 times greater than the extension of the second conductive section, measured in the same direction.

Preferably, the first conductive section and the second conductive section have the same thickness measured in a direction perpendicular to the main extension plane. Alternatively, it is conceivable that the thickness of the first conductive sec tion is at least 5 times, preferably at least 10 times and most preferably at least 15 times greater than the thickness of the second conductive section. Such a compa rably thin second conductive section might be easily bended to simplify the access to the contact section in specific applications. It is also conceivable that the thick ness of the second conductive section is different from the thickness of the first conductive section.

In particular, the first conductive section is made from bare aluminum, i. e. an alu minium being not covered with nickel and/or tin. Thus, nickel and/or tin can be saved in the manufacturing process, since not the whole busbar, in particular the first conductive layer, is covered with nickel and/or tin. Instead only the second conductive layer forming a part of the busbar is covered with nickel and/or tin. In particular, it is provided that the first conductive layer is connected to the second conductive layer directly. It is obvious for the skilled person that the bare aluminum sheet representing the first conductive section can be covered with another mate rial, for example by the isolation layer, without nickel and/or tin. In particular, the covering with another material does not extend to a region, which is bonded to the second conductive section. It is also conceivable that the first conductive section is partially covered with nickel and/or tin.

Preferably, the second conductive section is covered with nickel and/or tin. Thus, it is possible in an advantageous manner to establish the covering of the nickel and/or tin by a diving process and/or electrochemically. By completely covering the second conductive section, the manufacturing process of covering is simplified. At the same time by using a comparably small second conductive section, it is possi ble to restrict or limit the part being covered with nickel and/or tin in the finished state of the busbar.

Preferably, it is provided that in addition to the laser-welding seam, established by the laser-welding, a form-fitting between the first conductive section and the sec ond conductive section is realized, in particular in a direction parallel to the main extension plane. As a consequence, the mechanical strength of the connection be tween the first conductive section and the second conductive section is increased in an advantageous manner.

Preferably, the form-fitting is realized by a first curvature, bordering at least par tially the first conductive section in a plane parallel to the main extension plane, and a second curvature, bordering at least partially the second conductive section, wherein the first curvature and the second curvature are shaped complementary to each other. In particular, the first curvature and the second curvature interlock with each other to realize and/or to establish the form-fitting connection between the first conductive section and the second conductive section. Preferably, the laser welding bond or seam is realized along the first and second curvature. Thereby, it is conceivable that the modification of the first or second curvature, intended to re alize the form-fitting, might be established in a direction parallel to the main exten sion plane and/or perpendicular to the main extension plane.

Furthermore, a laser-welding seam, in particular a single laser-welding seam, is generated

- by directing a laser beam on a top surface of the first conductive section or of the busbar, and optionally by directing another laser beam on a bottom surface of a first conductive section or of the busbar or

- several laser-welding seems are generated by directing a laser beam on the top surface of the busbar or the first conductive section and by directing another laser beam on a bottom surface of the first conductive section or of the busbar. By treat ing the interface region between the first conductive section and the second con ductive section from both sides, i. e. at the topside and the bottom side of the bus bar, it is advantageously possible to increase the welding strengths and therefore the mechanical strengths of the bond between the first conductive section and the second conductive section. In particular, the method includes also an embodiment, which uses only a single laser, wherein the laser beam is split into two different la ser beams, wherein one laser beam is directed to the top surface and the other la ser beam is directed to the bottom surface of the interface region between the first conductive section and the second conductive section. By directing laser light onto the topside and the bottom side of the busbar or the interface section it is further advantageously possible to accelerate the bonding process, since the laser weld ing seam is generated simultaneously from both side, namely from the top side and the bottom side.

Preferably, the contact section includes an opening, in particular for inserting a corresponding pin or terminal. Thus, the opening allows connecting the contact section and therefore the busbar to an external component, such as a terminal of a capacitor, IGBT and/or a cable that transfers the electric current from the busbar to a device, which needs the current. Especially, capacitors are connected with the busbar by terminals, using bolts and nuts, for example. Preferably, the laser-weld ing bond is spaced from the contact section. As a consequence, the laser process is simplified, since the access to the interface section between the first conductive section and the second conductive section is improved.

In particular, the second conductive section is inserted into a recess of the first conductive section. As a consequence, a contact section can be incorporated in side or within the first conductive section or, in other words, in the middle of the busbar. For example, the recess represents a hole that reaches through the whole first conductive section. Alternatively, it is also thinkable that the recess has a stepped shape and the second conductive section is inserted into the step-shaped recess formed in the first conductive section.

Preferably, the second conductive layer is arranged adjacent to the first conductive section. As a consequence, it is possible to realize a terminal at the outside or at the outer edge of the first conductive section by connecting such a second con ductive section to the outer edge or outer rim of the first conductive section.

In particular, it is provided that a nickel plating and/or a tin plating is provided to cover the second conductive section is performed, wherein the nickel plating and/or the tin plating has a thickness between 1 pm and 50 pm, preferably be tween 2 and 25 pm and more preferably between 5 and 15 pm. It turned out that for said thicknesses an effective corrosion and oxidation protection can be real ized, without spending too much nickel and/or tin for realizing said protection.

Preferably, a laser power is adjusted for defining a length of the laser welding seam. Thus, it is advantageously possible to control the strength and dimensions of the generated laser welding seam. Alternatively or additionally, it is conceivable to adjust a treatment duration, during which the laser welding seam is generated, for adapting the dimensions and/or the form of the generated laser welding seam. Another aspect of the present invention concerns a busbar having a contact sec tion, in particular realized by a method according to the present invention, compris ing

- a first conductive section made from aluminum;

- a second conductive section made from aluminum, wherein the second conduc tive section includes the contact section or is connected to the contact section and wherein the second conductive section is at least partially covered with nickel and/or tin, and

- a laser welding bond connecting the first conductive section and the second con ductive section. All specifics being mentioned in the context of method according to the present invention apply analogously to the busbar being connected to the contact section and therefore having the contact section.

Another aspect of the present invention concerns a power distribution system hav ing a busbar according to the present invention. All specifics and benefits being mentioned above apply analogously to the subject matter of the power distribution system and vice versa. An example for such a power distribution system is a bat tery package or components being used in electrical vehicles, hybrid vehicles, rail vehicles and for generating or handling renewable energy.

Wherever not already described explicitly, individual embodiments or their individ ual aspects and features can be combined or exchanged with one another without limiting or widening the scope of the described invention, whenever such a combi nation or exchange is meaningful and in the sense of this invention. Advantages which are described with respect to one embodiment of the present invention are, wherever applicable, also advantageous of other embodiments of the present in vention. In the drawings:

Fig. 1 schematically shows a connection between a busbar and a con tact section according to a first preferred embodiment of the present invention,

Fig. 2 schematically shows a connection between a busbar and a con tact section according to a second preferred embodiment of the present invention,

Fig. 3 schematically shows a connection between a busbar and a con tact section according to a first preferred embodiment of the present invention n,

Fig. 4 schematically shows a connection between a busbar and a con tact section according to a first preferred embodiment of the present invention,

Fig. 5 schematically shows a connection between a busbar and a con tact section according to a first preferred embodiment of the present invention,

Fig. 6 schematically shows a connection between a busbar and a con tact section according to a first preferred embodiment of the present invention,

In Fig. 1 a busbar 1 , being connected to a contact section 20 according to a first exemplary embodiment of the present invention is illustrated. Preferably, such busbars 1 are used to collect and to transfer comparably high currents, preferably in a power distribution system. For example, such power distribution system and/or the connection of the busbar is used in an electro-motoric driven vehicle, electric locomotive or power transmission system. The contact section 20 is in tended to allow a contact to an external component, in particular, to transfer a cur rent from the busbar 1 to a cable. Preferably, the contact section 20 forms a termi nal. For example, the contact section 20 includes at least one opening 21 for con nection terminals (not illustrated).

To provide a comparably light busbar 1 it is preferably provided to use aluminium as material for the busbar 1. However, using aluminium as material for the busbar 1 makes a corrosion protection necessary to avoid a corrosion of the busbar 1. In particular, it is known to use nickel and/or tin for covering the busbar 1 for provid ing the desired corrosion protection. However, covering the whole busbar 1 with nickel and/or tin, in particular, performing a nickel and/or tin plating of the alumin ium busbar 1 is a material- and cost-intensive way to create the corrosion protec tion of the busbar 1.

Especially, it turned out that it is sufficient for the corrosion protection, if the cover ing of the busbar 1 with nickel and/or tin is established in the near of the contact section 20 and/or in the contact section 20, since this region is receptive for corro sion. Therefore, it is reasonable to create or to establish the covering only partially at the busbar 1 , in particular in a region being closed or next to the contact section 20 and/or in the contact section 20. However, covering the busbar 1 only partially with nickel and/or tin leads to challenges in manufacturing, which has to be over come. It turned out that it is an advantageous way to realize in a simple and effec tive manner the partial covering of the bus bar with nickel and/or tin by using a first conductive section 11 and a second conductive section 12, the second conductive section 12 including the contact section 20 and/or is connected to the contact zone 20. Thereby, the second conductive section 12 forms a part of the busbar 1 in a finished state of the connection between the contact section 20 and the busbar 1.

In particular, it is provided to use a flat body, mainly extending along a main exten sion plane HSE as a second conductive element 12 in order to continue the gen eral cause of the first conductive layer 11 for forming a flat or laminated busbar 1. Furthermore, it turned out to be beneficial to use a laser-welding process to per form a bonding and/or to establish a connection between the first conductive sec tion 11 and the second conductive section 12. In the embodiment illustrated in fig ure 1 , the second conductive section 12 forms a lug protruding from an outer edge of the first conductive section 11. It is also conceivable that the second conductive section 12 is at least partially inserted into a recess being formed at the outer edge of the first conductive section 11 of the busbar 1. As a consequence, a contact surface, i.e. an interface section, between the first conductive section 11 and the second conductive section 12 is increased to strengthen the connection or bond between the first conductive section 11 and the second conductive section 12.

In Fig. 2 a busbar 1 connected to a contact section 20 is illustrated according to a second exemplary embodiment of the present invention. In general, the embodi ment illustrated in figure 2 differs from the embodiment illustrated in figure 1 by us ing a form-fitting interaction between the first conductive section 11 and the sec ond conductive section 12 in addition to the bond realized by the laser welding seam 10. For establishing the form-fitting connection between the first conductive section 11 and the second conductive section 12, in particular in a direction per pendicular to the outer edge of the first conductive section 11 and parallel to the main extension plane HSE, the first conductive section 11 has a first contour and the second conductive section 12 has a second contour, the first conductive con tour and the second contour having a complementary shape, in order to be con nected with each other in a form-fitting manner, in particular in a direction parallel to the main extension plane FISE. Preferably, the first conductive section 11 and second conductive section 12 are connected by a dovetail-joint. As a conse quence, the mechanical strength and connection between the first conductive sec tion 11 and the second conductive section 12 is improved.

In Fig. 3 a busbar 1 being connected to a contact section 20 is illustrated accord ing to a third preferred embodiment of the present invention. The embodiment il lustrated in figure 3 differs from the embodiment illustrated in the figures 1 and 2 mainly by the arrangement of the second conductive section 12. While in the em bodiments illustrated in the figures 1 and 2, the second conductive section 12 be ing located adjacent to the first conductive section 11 , the second conductive sec tion 12 in the embodiment illustrated in figure 3 is located inside of the first con ductive section 11. In particular, the second conductive section 12 is inserted into a corresponding recess being formed in the first conductive section 11. For exam ple, the first conductive section 11 has a round recess or hole, which allows insert ing a correspondingly shaped second conductive section 12 into the recess. In particular, it is provided for all embodiments, in particular those, which are dis closed or illustrated in the figures 1 to 3 such that the location of the welding seam 10 is spaced from the contact section 20, preferably more than 1 mm, more prefer ably more than 10 mm and most preferably more than 100 mm. This simplifies the manufacturing process, because the region, which has to be treated by the laser- light for forming the laser-welding bond or seam 10 has an easier access to an in terface section between the first conductive section 11 and the second conductive section 12, in particular, compared to a situation, in which the contact section 20 is directly connected to the busbar 1 , i. e the first conductive section 11. This is an other benefit of using the second conductive section 12 as an intermediate ele ment between the first conductive section 12, i. e. the main part of the busbar 1 , and the contact section 20.

In Fig. 4, a busbar 1 connected to the contact section 20 is illustrated according to a fourth preferred embodiment. The embodiment illustrated in figure 4 differs from the embodiment illustrated in figure 3 mainly by the shape and design of the con tact section 20 and/or the second conductive section 12. In particular, it is provided that the contact section 20 in figure 4 has three openings 21 being located in a row. As a consequence, the contact section 20 is no longer formed circular or round and instead has an elongated shape, in particular along a direction being defined by the row of the openings 21. In Fig. 5 a busbar 1 being connected to a contact section 20 is illustrated accord ing to a fifth exemplary embodiment of the present invention. In particular, the em bodiment illustrated in figure 5 refers to an embodiment having a connector ele ment 13, 14, which establishes the contact section 20 being connected to the bus bar 1. In particular, the contact section 20 is formed as a bushing, i. e. as a cylin drical shaped body that protrudes from the busbar 1 in a direction being perpen dicular to the main extension plane HSE of the busbar 1. Such a bushing or cylin drical shaped connector element 13, 14 has an opening 21 for receiving a pin, for example a pin of a capacitor, which is connected to the busbar 1. As illustrated in figure 5, the bushing or the cylindrically shaped body might have a first part 13 and a second part 14, wherein the first part 13 reaches through a hole or recess inside the second conductive section 12 and in particular reaches through this hole or re cess for being connected with the second part 14 in order to fix the bushing or the cylindrical shaped connector element 13, 14 to the busbar 1 in a form-fitting way, preferably in a direction being perpendicular to the main extension plane HSE. Preferably, the bushing is connected to the second conductive layer 12 also by a laser-welding or they, i. e. the second conductive section and the connector ele ment, form a single or monolithic body. It is also conceivable that the bushing is made from aluminium and/or is covered with nickel and/or tin.

Fig. 6 shows a connection between a busbar 1 and a contact section 20 according to a sixth preferred embodiment of the present invention. In particular, it is pro vided that this embodiment refers to a busbar 1 has a stripe-like shape. In particu lar, it is provided that the first conductive section 11 and the second conductive section 12 have the same width measured in a direction of a general course of the interface section between the first conductive section 11 and the second conduc tive section or mainly parallel to the direction along which the laser welding seams 10 extends. The shape of the first contour of the first conductive section 11 and the second contour of the second conductive section 12 corresponds to the one, which has been discussed in figure 2. Reference numbers:

1 busbar

10 seam 11 first conductive section

12 second conductive section

13 first part

14 second part

20 contact section 21 opening