34 March/April 2024 | E-Mobility Engineering because e-vehicles do not produce the same noise as a combustion engine, but inside, the focus switches to the acoustics of the electric drivetrain and operating noise. To cut vibration noise, there are several dry-lubricating, bonded coatings in the form of polymer systems based on PTFE, PFA or FEP fluoropolymers, as well as MoS2 or graphite. This helps reduce the contact noises caused by vibration by using flock coating, with cathodic dip coating (KTL) as the base layer. Further advantages of the pure flock coating are the compensation of manufacturing tolerances, and noise insulation on metal and plastic surfaces. However, when using 48 V, the operating temperature of fasteners rises to over 160 C, meaning that for safe operation, silver coatings in thicker layers must be deposited on the components. A professional coating is also crucial for the safe operation of large vehicle batteries, because efficient protective devices, such as corrosion-protected housings, can only be created with high-quality surface technology. The transmission of high-frequency signals in the vehicle is often overlooked and the coatings of various components can reduce the impact of interference sources. A multi-layer structure allows static charges to be selectively dissipated and signal transmission interference to be reduced, while also providing electrical insulation. Fire protection Most engineering plastics meet fire requirements at thicknesses of 1 mm. However, the rising number of electrical components with a high-power output is increasing demand for flame-retardant thermoplastics. With the popularity of electric cars and the potential danger of thermal runaways, the automotive industry headed towards different standards that were mainly designed for stationary applications. Those standards are mainly described in the Underwriters Laboratories Standards UL 94 and UL 746 (see Standardisation and ratings). The intention of applying these standards is to prevent an electric malfunction causing a fire from parts in the vicinity of the battery cells. With appropriate materials in place that are resistant to short-time ignition sources, the outbreak of a battery cell fire triggered by external malfunctions is less likely. The sources of ignition are typically high current arcs, hot wires and fusing transistors or capacitors. Flame-retardant plastics are useful in the following e-mobility applications: in the vicinity of sensitive materials, such as battery cells, to prevent thermal runaways; components with a high potential for ignition due to nearby electric currents, such as breakers and switches; and in EV charging cables (cable sheathings) for increased safety and the prevention of fire propagation. Overload, improper use, and manufacturing and assembly errors, such as defective soldered points or loose connections, all constitute real fire hazards. The aim of technical fire safety in the eventuality of a malfunction is to prevent the ignition of the component and stop flames spreading to the immediate surroundings. In certain cases, an additional requirement exists that the housing must not catch fire if exposed to an external source of ignition. The technical fire-safety requirements are described in special safety regulations for electrically operated devices and installations. The measures required are meant to ensure the safety objective is achieved. This includes measures of a structural nature, such as the limitation of temperature in case of malfunction or the use of materials with a low level of ignitability and flame spread. 48 V hybrid The design of the battery pack for 48 V hybrids is key, and thermoplastics are vital here. The battery is small and cost-effective due to passive cooling. The challenge of a plasticencased battery is to handle the load while cells expand over the life of the battery. This is achieved through a unique arrangement of the cells within the housing that incorporates passive cooling. For example, a 14 kW hybrid 48 V battery with a nominal energy of 360 Wh weighs under 6 kg and measures 300 x 175 x 90 mm. The Focus | Polymer considerations for EV A 48 V battery pack using thermoplastic (Image courtesy of Bosch)
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