Abstract
Li-ion battery safety in electric buses is critically affected by rollover accidents, which can cause severe deformation of the bus superstructure. Such deformation may cause internal short circuits and trigger thermal runaway. In this context, this work investigates how different propulsion modes affect the safety of a bus superstructure under a rollover scenario in accordance with UNECE Regulation No. R66.02. This work studied an internal combustion engine (ICE) and electric propulsion systems, using the ICE chassis as the base for the electric bus. The study defines worst-case scenarios for both vehicle types, determines the center of gravity (CoG), and performs numerical simulations using the finite element method. The ICE and electric buses have CoGs of 5397.5 × 13.0 × 1617.4 and 4474.1 × 20.9 × 1682.2 mm, respectively. The ICE vehicle had a total weight of 15,836 kg and a reference energy of 5.0580 × 105 kg·m2/s2, while the electric vehicle had a total weight of 18,118 kg and a reference energy of 5.1145 × 105 kg·m2/s. For the rollover simulations, the unstable positions before tilting were set to 33.7° and 35° for the ICE and electric vehicles, respectively, and the models were rotated to ground contact at angular velocities of 1.75 and 1.79 rad/s. The results indicate that the ICE vehicle satisfied the regulatory requirements. However, the electric vehicle exhibited intrusion of up to 32 mm into the residual space when the same ICE structural concept and passenger configuration were applied. Therefore, some modifications were proposed, including capacity adjustments and alternative battery systems, to preserve the residual space during the rollover scenario. These results highlight the need to account for electric bus specific characteristics rather than directly converting ICE chassis designs.
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