Electric Bus Chassis Design Optimisation with Integrated Battery: A Rapid Hierarchical Design Workflow
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Integrating the traction batteries into the chassis of an electric bus couples the frame layout, the battery positions and the structural requirements. This paper presents an automated workflow that takes a battery-integrated chassis module from a density-based concept to a detailed thin-walled design. A three-dimensional topology optimisation and the battery brackets define a one-dimensional ground structure of rectangular hollow sections, which is reduced and sized for strength, stiffness and fatigue. A Kriging surrogate model optimises the battery positions and regenerates the ground structure, and therefore the frame topology, for every candidate position. The frame is then converted into a shell model with gusseted joints (member ends connected by gusset plates) and sized to standard plate thicknesses; all analyses use Altair OptiStruct. For a bus mid-frame module (the chassis section between the sub-frames) with three battery packs and thirteen load cases, the verified design at the nominal battery positions is 8% lighter than a ladder frame and 27% lighter than a braced ladder frame designed with the same procedure; this order holds for all fatigue requirements examined. The battery placement reduced the sized one-dimensional frame mass by up to 7%, but this gain was not retained in the detailed shell model, in which the joints add mass. The chain that produced the final design requires about 17 minutes of solver time.
