With their predominantly rectangular conductor cross-sections, busbars in oil-cooled electric motors, cooled batteries, oil pumps and air conditioning compressors place special demands on sealing technology. At the same time, it is crucial for the sensitive power electronics to be reliably protected from media such as oil. What makes this problematic is the geometry of the busbars, which are stamped out of copper or aluminum sheets and then formed into the desired shape. The resulting rectangular cross section is superior to a round one in that several busbars can be placed very close together to save space. This is an important advantage, not only in battery production, where every millimeter of installation space counts.
Until now, it has not been possible to reliably seal rectangular busbars with standard seals or potting solutions. One reason is that the deviating thermal expansion coefficient of the copper can cause stress cracks in brittle adhesives during use. In addition, conventional seals are unsuitable for rectangular cross-sections, which can result in leaks and consequently damage the power electronics of electric vehicles.
Firmly bonded connection of all components
To prevent this, Freudenberg Sealing Technologies has developed a rectangular busbar overmold that is impermeable to media and seals reliably while also combining multiple sealing functions if needed. This innovation utilizes an elastomer layer that is applied to the rectangular busbar by chemical adhesion and firmly bonds with the metal conductor. In a next manufacturing step, the elastomer cross-links with the surrounding thermoplastic during injection molding. Ideally, the elastomer layer consists of vulcanizable elastomers such as FKM, AEM, ACM, HNBR, NBR, and EPDM, although thermoplastic elastomers (TPE) can also be used. The flexible coating does even more than provide a reliable seal, it also reduces the notch effects along the edges of the conductor, which makes the electronic component less susceptible to stress cracking.
High temperature and media resistance
With their extensive materials and industry knowledge, the experts at Freudenberg Sealing Technologies can identify the appropriate material for every application and sealing requirement. Here the materials offer higher temperature resistance than conventional solutions on the market. They reliably withstand temperatures well above 120 °C. Sealing materials from Freudenberg Sealing Technologies are also well in the lead in terms of media resistance. Immersion tests in customer-specific media ensure that the seals perform their function throughout their service life, even under extreme conditions.
The choice of material depends on the surrounding media and the prevailing temperatures. By using a special seal design and choosing appropriate materials, it is even possible to integrate additional sealing functions into a module. As a result, fewer components are required, which reduces the complexity of the application. In addition, the Freudenberg sealing specialists can conceive the sealing material and design in such a way as to compensate for tolerances in the axial and radial directions, for example. “The tolerance compensation prevents cracks and leaks that could be caused by fixed and rigid connections and thus increases the service life of the application. It also makes the assembly much easier,” says Parisa Burger, Director Strategic Business Development and Project Manager at Freudenberg Sealing Technologies.
Thanks to its high-level materials and processing expertise, Freudenberg Sealing Technologies offers a reliable seal for rectangular busbar overmolds that are impermeable to media. As a result, it efficiently protects the power electronics of electric vehicles against leaks.
Flame protection in batteries is another relevant application area for special materials. Thermal runaway of one or more cells may lead to a short circuit in the busbar, which in a worst-case scenario may trigger a thermal event that can no longer be controlled.
Freudenberg Sealing Technologies now offers integrated solutions for insulation and flame and particle protection in a single product to Battery manufacturers. The product portfolio ranges from overmolding busbars and tapes to covers in complex geometries. Depending on the cell chemistry used by individual manufacturers, the sealing expert has developed materials that both insulate and protect against the high temperatures and particles that may occur during cell fires.
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