As a specialist in sustainable transport, Streetscooter GmbH has developed an electric vehicle for letter and package delivery for Deutsche Post. Safety played an important role in development. In the event of a crash, not only occupant safety needed to be assured; all safety-relevant, high-voltage components also needed to be housed in such a way that they are guaranteed protection in an accident. Streetscooter joined forces with CAE development partner TECOSIM to calculate and simulate different crash scenarios.
Engineers at the company simulated different frontal impacts and were required to take into account aspects such as the design concept, structural rigidity, vehicle weight and costs. Streetscooter and TECOSIM were then able to develop a crash-optimised vehicle body together based on the CAD design and calculation results, which is now being successfully manufactured in a pilot production run.
Danger - High voltage!
The Tecosim calculation engineers subjected the design to load conditions in accordance with statutory regulations ECE R94 and ECE R12, that is to say: frontal impact with flexible barriers and frontal impact against rigid walls. Such accident scenarios in vehicle development present particular challenges when it comes to electrical vehicles. The accident-proof housing for the high-voltage components was a key element in the design since it was essential to ensure that risk to occupants and damage to the rechargeable battery are prevented. The high-voltage battery is now enclosed beneath the driver's cab in the vehicle floor, where a steel cage protects it from deformation.
The CAE specialists at Tecosim not only focussed on safety during the vehicle body optimisation. They also needed to strike a balance between structural rigidity and crash performance while also keeping an eye on the vehicle's weight and costs. Streetscooter's design concept stipulated that the number of materials, sheet thicknesses and configurations needed to be kept to a minimum, thus reducing costs for procurement and warehousing.
Using FE calculations, the Tecosim engineers proposed different solutions to select material grades and thickenesses. The use of high-strength steels ensured that the material thickness and, consequently, also weight are reduced while also improving crash performance. In addition to changes in the shape, localised strengthening was introduced to enhance crash behaviour. Besides an optimised reinforcing seam in the main chassis beam, this also included a crash-proof reinforcement of the battery protection cage and an optimised link between the load bed and the driver's cab. The result is a comparatively lightweight vehicle body design which keeps production costs within the proposed limits while also meeting all security requirements.
"Safety is a top priority for Streetscooter," declares Ugo Fabrizio Scelsi, Complete Vehicle Project Manager at Streetscooter. The company decided to comply with frontal impact requirements as per ECE R94, thus providing a higher safety standard, even though this is not required under law for lightweight Class N1 electric vehicles. "Thanks to virtual crash simulation and the effective cooperative partnership with Tecosim, we managed to optimise crash behaviour in the vehicle body in a very short period of time and, what's more, before a prototype was produced or cost-intensive, real-life testing was carried out. We are very please with the result."
In 2011, Deutsche Post AG commissioned Streetscooter GmbH to develop a design concept for an electric vehicle for letter and parcel delivery which was to meet the following requirements:
Special design concept for short distances (less than 100 kilometres)
Able to withstand 200 stops and restarts per day
For use up to 300 days a year
No high speeds required
Sufficient load capacity for letters and parcels
Robust features which comply with all safety requirements
The first prototype based on the design concept has been in development since autumn 2012; fifty pilot run vehicles are to be tested during delivery operations this year. Low volume production is planned for mid-2014.