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

dedicated architectures. Karkare says, “Clean-sheet designs allow engineers to package battery packs more optimally and permit better structural stability from both the vehicle dynamics and manufacturing perspectives.” Unsurprisingly, clean-sheet designs offer the best opportunities to optimise a vehicle’s weight distribution and packaging with its dynamic performance in mind. As well as much greater freedom in positioning the heavy energy storage and drivetrain components, says Porsche Engineering, it also allows the design team to find the best chassis kinematic points. Kinematics is the study of the motion of points, objects and groups of objects – suspension mechanisms, for example – in isolation from the motion’s causes. With the goal of keeping the tyres in contact with the ground as consistently as possible, it is essential to optimise the motions of the suspension linkages in the volume available. The suspension pick-up points influence the geometry and orientation of basic components such as control arms and linkages that constrain the movement of the wheels. Pick-up points are therefore key kinematic points and must be located on nodes on the chassis; these are points that remain stationary as the chassis flexes and vibrates, which even the strongest and stiffest do to a degree. In terms of the effect on handling, a 50/50 weight distribution is favourable but not mandatory for a well-balanced vehicle, according to Porsche Engineering. That is because the dimensions of the front and rear tyres can usually be adjusted to compensate for differences in load between the axles. AVL agrees, adding that the best solution often emerges from considering the application and permissible additional load. Rear- biased distributions of 45/55 or even 40/60 might prove better for traction and agility in rear-wheel-drive sportscars in particular, enabling them to brake later on the approach to corners because the rear wheels lock later. Also, the load transfer from rear to front under braking can bring the distribution to 50/50 dynamically. Load transfer More important though than the distribution of load between axles, Porsche Engineering adds, is the fore/ aft location of the large masses and the height of the CoG. With a low CoG and a centralised mass, there is less load transfer laterally across the vehicle when cornering, and that allows the car to make better use of the available grip to generate more lateral g-force, which translates into higher corner speeds. The lower roll gradient allows softer anti-roll bars to be fitted, improving comfort, as do the reduced oscillations in pitch and roll in normal street driving. Also, inherently better agility and steering response permits a softer, more comfortable spring and damper set-up to be used without sacrificing performance. The greater weight of an EV can be an advantage in terms of comfort, AVL points out, because the extra weight of the battery is supported by the springs, suspension, wheels and tyres. These are relatively light, leading to a higher sprung-to-unsprung mass ratio and a smoother ride, principally because it increases the separation between the natural frequencies at which the body and the tyre/wheel/suspension system oscillate. Karkare adds, however, that greater weight also requires stiffer tyres, different shock absorber tuning and demands more from the braking system, which together can make the desired ride comfort a challenge to realise. Higher overall weight also puts greater demands on the tyres, which is an important safety consideration that impacts tyre performance specifications. Apart from the flexibility to engineer in favourable weight distribution, eliminating the IC engine also brings the opportunity to improve crash safety, Sundstrom says, because the design of the crumple zones is not constrained by the large, rigid block of the engine in front of the driver. Striking the right balance between handling, comfort and safety for passenger cars presents a number of engineering challenges; AVL points to the rearward shift in the CoG. In some front-wheel-drive (FWD) configurations, for example, this can present traction problems – particularly if the vehicle is fully loaded – which are exacerbated by the high torque and rapid torque response characteristic of electric motors. This can also exacerbate tendencies towards torque steer in FWD cars. Adding a large battery to an EV derived from an IC-engine platform also often results in a longer wheelbase and consequently a larger turning circle, even in smaller vehicles. AVL also says the rearward placement of a large battery pack can bring severe packaging problems in vehicles that use simpler rear In EVs, batteries must usually be squeezed into space no longer occupied by items such as propshafts and exhaust pipes, reducing the scope to optimise mass distribution (Courtesy of Volvo) 46 Autumn 2021 | E-Mobility Engineering