Lightweighting of a hydrogen fuel cell vehicle whilst meeting urban accident criteria

The aim of this paper is to assess the safety performance of a lightweight hydrogen fuel cell city concept vehicle entitled Microcab [1]. The Microcab is a lightweight 4 seat hydrogen fuel cell concept vehicle with a combined mass (excluding passengers) of less than 800kg. The Microcab has a range of 180 miles; it includes a hydrogen fuel tank pressurised to 350 bar. The research focuses on urban accident scenarios; including frontal, lateral and compatibility loadcases. All loadcases utilise urban speeds, i.e. speeds ranging up to 40km/h for frontal impacts. The crashworthiness of the Microcab has been analysed using explicit non-linear Finite Element Analysis (FEA). The study concludes that within the limitations of the material parameter definitions and mass distributions; the crashworthiness in connection with urban accident scenarios is good. This includes aspects such as vehicle compatibility loadcases and protection of the hydrogen fuel tank e.g. for intrusion. The outcome of the study also suggests structural refinements for the future Microcab final production model; with an aim of further improving the vehicles' crashworthiness. These refinements include raising the primary front crash structure to better align it with that of a Sports Utility Vehicle (SUV) as well as bracing the fuel cell area in case of a rear impact in order to better protect this vital component. It is also suggested that adhesive joints were suitable for structural crash integrity in all the loadcases studied within this paper, including low speed impact for repairability. A structural optimisation study has also been undertaken utilising Design Of Experiments (DOE), shape-size- and topology optimisation. DOE was employed to further improve the stiffness of the chassis with respect to safety, whilst minimising the mass increase. Topology optimisation models based on the maximum crash force magnitudes computed in the initial part of the study were also setup; the results of these suggested future changes to the Microcabs' floor layout could be utilised to further enhance the vehicles crashworthiness.