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
as the largest mass – the battery – is concentrated in the centre of the vehicle. “As most EVs use two electric machines, the control of the four- wheel drivetrain has a big influence on the dynamic behaviour,” says Martin Reichenecker, senior manager, chassis testing, at Porsche Engineering. “For both stability and handling, the linearity of the four-wheel drive [4WD] is important.” Simulation specialist AVL notes that increased weight brings a need for better weight distribution. Lowering the CoG in relation to the roll centre, as a result of the battery’s layout and position, increases the car’s stability in roll, although the extra weight puts larger loads on the chassis components. With the option to drive all four wheels independently, the company says, torque can be optimised at each one, and as the wheel torques are much higher in EVs than in comparable IC-engined vehicles, longitudinal acceleration tends to be much greater and spread over a wider speed range. That means other chassis components must be stronger to support the larger loads. “Although they are not directly responsible for dynamic behaviour, regenerative systems such as brake/ suspension energy recuperation need a trade-off between performance and recuperation, so the dynamics challenge is to optimise that trade-off,” AVL says. Piyush Karkare, director of global automotive solutions at Siemens Digital Industries Software, notes that the extra weight of the battery pack presents a challenge to ‘vertical dynamics’ – displacement and acceleration in heave. That affects comfort in particular, and drives different requirements for the tyres, particularly increased sidewall stiffness and for the suspension in terms of spring and damper tuning. He adds that traction control, along with control of suspension, brakes and steering, are all impacted significantly by the vehicle’s kerb weight and even more so by the distribution of both weight and propulsive power. “Overall drivetrain performance and control strategies have a direct effect on the dynamics of EVs,” he says. Peter Sundstrom, team leader for mechanics and vehicle dynamics at vehicle modelling specialist Modelon, agrees. He emphasises that as well as elevating family car acceleration to sportscar levels and pushing high-end EVs into supercar/hypercar territory, the rapid torque response available from electrical machines enables much more accurate slip control. That enhances traction and stability control, and torque vectoring, for further improvements in performance and active safety. Sundstrom also highlights packaging differences, noting that electrical machines take up less space than an IC engine and its transmission and final drive components, and therefore provide more freedom to optimise suspension design. The active systems also have an impact in this area, he says, adding that the use of regenerative braking provides an opportunity to reduce the size of the components in the hydraulic braking system. centre, the polar moment of inertia is lower and the dumb-bell is much easier to turn. According to Porsche Engineering, the CoG and the polar moment of inertia are two of the three most important criteria affecting an EV’s dynamic behaviour, the third being control of the drivetrain. The CoG tends to be lowest in battery EVs that use a skateboard-style architecture, while yaw inertia also tends to be low, ;Oe oWWortunity tOat electriÄcation Wresents to oWtiTise Tass distribution Oas beneÄted OiNO WerforTance roadcars sucO as tOe ;aycan (Courtesy of 7orscOe ,nNineerinN) :usWension and driveline RineTatic Todels can be custoTised to reflect any veOicle layout and raWidly iterated to oWtiTise ride and OandlinN virtually 9ed arrows sOow tOe y and a a_es (Courtesy of 4odelon) Autumn 2021 | E-Mobility Engineering 43 Insight | EV dynamics
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