ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

Seals and sealants perform a host of unsung but vital functions. Peter Donaldson explains the di erent types, their uses and the materials they are made from No entry or exit U nglamorous they may be, but seals and sealant materials nonetheless play an essential role in all modern vehicles, keeping contaminants out and fluids in, and are used in the vast majority of systems and components. The engineered polymer compounds of which seals are made must resist heat, vibration, dust, fluid and chemical attack for years and tens of thousands of miles, while being easy to apply during manufacture and complying with health & safety and environmental regulations. The most prominent application in EVs is sealing a battery pack housing, followed by gasketing for power conversion electronics such as inverters, along with motors and other components of an electric drivetrain. All the high-voltage connectors must be sealed, as must the main battery box, module and cell enclosures, plus the lines and connectors in fuel cell systems, electrically driven accessories, the thermal management system serving the battery, motors and charging system. Thermal management systems often feature complex multi-way valves, while conductive cooling matrices must be sealed and cooling plates bonded to cells with materials that also conduct heat efficiently. Safety-related systems that often feature hydraulics, such as brakes and ride control systems, also require sealing and often usually include pumps that generate significant amounts of pressure that pose a challenge to the seals. Rapid rotary seals Electric motors in EV applications spin faster than in IC engines, so rotary seals have to cope with higher surface speeds. Most IC engines rev to no more than 7000 rpm, although some sportscars rev faster and many bikes reach 15,000 rpm or more. By contrast, an EV motor spinning at 15,000 rpm would be at the low end of its range, with 20,000 rpm being typical and 30,000 rpm not unheard of. As surface speed is derived from rpm and shaft diameter, the resulting speeds can be high. To give an extreme example, a 30 mm shaft spinning at 30,000 rpm produces a surface speed of a little over 47 m/s, or nearly 170 kph. While seals in IC engines tend to be generously lubricated by engine oil, those in electric motor applications get very little lubrication, often running either a fine oil mist or in a dry environment. What’s more, the need to maximise range in road-going EVs results in efforts to keep friction to a minimum. This combination of high surface speeds, poor lubrication and the need for minimum friction makes sealing a challenge. In an extreme case like the one above, PTFE would be an appropriate material choice, as it offers good heat resistance and low friction, even if it is relatively expensive. In EVs, electrical conductivity and flame resistance are, depending on the exact application, either new requirements for sealants or are more important than they were in IC-engined Battery packs present demanding sealing requirements to prevent contamination from the outside, to seal in electrolytes and coolants and to keep them separate (Courtesy of Henkel) 64 Autumn 2021 | E-Mobility Engineering