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

Mass distribution di erences When it comes to how much the nature of the drivetrain influences mass distribution by dictating where the major components must go, Sundstrom imagines a scale starting with IC-engined vehicles at the rigid end through hybrids and fuel cell EVs to battery EVs at the most flexible end. This is controlled by the size and weight of the components and the manner in which they are connected. “With a combustion engine, you are pretty much locked down in terms of where you put your mass, but with a battery EV there is basically just cabling connecting them together, so you get more freedom to put the mass where you want it for the vehicle’s dynamic behaviour.” Most IC vehicles are front-engined for convenience of packaging (mid- and rear-engined cars being a tiny minority) but in all cases the size, weight and cooling needs of the powerplant mean its position dominates the architecture of the car. The fuel tank, which is normally at the rear, is a mass that varies as it empties and is refilled, and that has to be accounted for, Siemens’ Karkare points out. While hybrids must pack even more machinery into the available volume, there are differences among them in terms of mass distribution that stem from powertrain layout, according to AVL. Some place the additional weight of an electric motor between the IC engine and the gearbox, for example, while others use an e-axle at the rear and turn a front-wheel-drive IC car into a 4WD hybrid. They also need space for the battery, usually within a vehicle architecture conceived for an IC engine, so the modules are usually fitted into the ‘transmission tunnel’ or in the rear compartment. Sometimes they are positioned above the CoG, Porsche Engineering notes, reducing agility and performance. A series hybrid, however, is usually more like an EV fitted with a range extending generator than an IC- engined vehicle with electrical machines integrated into its powertrain. As the range extender is likely to be small and deliver its power entirely electrically, there are more options for positioning it. The layout and mass distribution of fuel cell EVs are similar to those of hybrids, in AVL’s view. Both need smaller batteries than battery EVs, and they are usually located behind the rear axle. Both also need fuel tanks, with a fuel cell EV needing to store hydrogen gas at high pressure, often just in front of the rear axle. Also, in a fuel cell EV the under-bonnet space is typically occupied by the fuel cell stack, power conversion electronics and the electric motor. With battery EVs, the electric motor and simple transmission are outweighed – literally – by their massive battery packs, which makes them the heaviest category of all. At the same time though, they bring the CoG lower and closer to the roll centre, shortening the effective moment arm and reducing the tendency to roll. While battery EVs benefit from a lower CoG, their mass distribution is often oriented toward the rear because of the location of the battery and electric drivetrain components, Porsche Engineering says. Clean-sheet advantages Among battery EVs, there is a distinction between those based on a conventional IC-engine platform (or one available in both IC and battery EV variants) and clean-sheet battery EV designs. “If you base an EV on a traditional platform, you tend to just place the motor where the IC engine was and the battery probably somewhere around where the fuel tank was,” says Sundstrom. “So you essentially get the same mass distribution but probably a heavier car.” That is because battery EVs based on IC-engine layouts suffer from packaging obstacles owing to an architecture conceived for another powertrain concept. The spaces left for the IC-engine components such as exhaust systems are no longer used for them, causing difficulties in positioning batteries and e-axles because of complex underbody topology. AVL says, “That means very expensive and complex battery layouts have to be adopted, and a massive variation in the CoG occurs, which moves further to the rear. If the e-motor then sits in the front and the battery mainly in the back, this causes a major limitation in performance.” Typically, therefore, it is more common for IC-engined and hybrid vehicles to share platforms with battery EVs that increasingly are built on 7owertrain dynaTic beOaviour diɈers siNniÄcantly between 0C enNined veOicles and ,=s owinN to tOe raWid torXue resWonse of electrical TacOines (Courtesy of (=3) 44 Autumn 2021 | E-Mobility Engineering Insight | EV dynamics