Thought given to material selection and component design has kept weight down on this new electric vehicle. Jon Lawson finds out how it was done
Thought given to material selection and component design has kept weight down on this new electric vehicle. Jon Lawson finds out how it was done.
If you were tasked with designing a small autonomous vehicle perfectly suited to urban mobility, what material would you opt for to ensure its lightness? Aluminium? Composite? How about steel?
That’s the main construction material of choice for the appropriately entitled Steel E-Motive autonomous ride-sharing concept electric vehicles (EVs) created by WorldAutoSteel, a consortium consisting of 18 industry firms.
Intended to offer mobility as a service for four passengers in the short wheelbase version, or up to six with the larger version, the machine is a response to increasing urbanisation and a desire to reduce pollution and save commuters money.
George Coates, Technical Director at WorldAutoSteel says, “Because steel has been around for so long in the auto industry some may feel it’s old-fashioned. Nothing could be further from the truth, we speak to OEMs and universities all the time and because the material now offers so many properties there is a resurgent interest.”
So exactly how has the use of steel contributed to making this vehicle light? Coates explains, “We have access to a portfolio of 64 different grades of advanced high-strength steel (AHSS) and we were able to use 12 different thicknesses of material for the vehicle. For some sections where we wanted extreme lightweighting we were able to go as thin as 0.5mm because of the very high strength properties. We are also using a variety of different fabrication processes, other than conventional stamping, so we are using roll forming, roll stamping, hydroforming and hot stamping, these processes allow the metal to be thinly produced very uniformly offering greater ductility and design flexibility.”
The battery carrier structure is a good example of this philosophy, being 37% lighter than an equivalent benchmarked unit with only three quarters of the manufacturing cost. Coates explains, “It’s lighter because of a combination of material choice and design. Rather than just make a box, the upper part of it is actually the floorpan and the lower part is a frame assembly made of crossmembers, longitudinals and a 3-piece bottom plate. What this does is eliminate several different parts in the structure. We’ve used these techniques in the design of the doors, by eliminating the B pillars and replacing them with tubes inside the door, creating a mass saving. Because of the scissor design of the doors, we were able to eliminate the entire body-side outers.”
Another aspect of the vehicle’s design concerned the roof, where the consortium also managed to shave off a few pounds. “Glazing isn’t light,” confirms Coates. “However, we looked closely at the roof design and came up with what we call the ‘Union Jack’ where design and styling worked together to create an exoskeleton look, and by selecting the right grades of steel we managed to save mass, use less steel overall and create an open, airy cabin atmosphere.”
It was in keeping with the original design brief that passengers didn’t feel claustrophobic in what is ultimately a relatively small vehicle.
Speaking of passenger comfort, thought has been given to acceleration and deceleration characteristics, what Coates refers to as “drive-cycle smoothing.” What’s more, the simulations which have been performed based on the vehicle having connectivity to other vehicles and infrastructure (such as traffic lights) show a 15% reduction in emissions.
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Coates observes, “When it comes to lightweighting the philosophy was simply to use smart applications of the different steel grades available. Given the strength levels we had access to, we’ve certainly been able to take mass out of the structure. Also, with the optimisation routines available via CAD, CAE and simulation tools like AutoForm, we relied on all the typical engineering tools to keep the weight down. On this project we didn’t spend a lot of time with artificial intelligence, but this is going to become a major element in the design of future vehicles, as it matures and becomes more efficient it will help us make better decisions about where mass is located on-board. Also less waste at the production stage reduces the vehicle’s overall carbon dioxide footprint, which is becoming much more important with OEMs today, who are beginning to account for and report life-cycle emissions. This is where steel applications win, because we produce between one seventh and one twentieth fewer emissions during production compared to alternative structural materials.”
The project has moved beyond the modelling stage, and a quarter and one third scale mock-ups have been 3D printed to tour the world’s engineering shows. Coates reports lots of interest from manufacturers keen to enter the robo-taxi market. “Because the thing is fully developed at a concept level,” he notes, “Companies can pick and choose the bits they want. This is especially important for start-ups who can save months in design time. We have come together to produce a detailed 500-page engineering report so interested parties can download it free-of-charge to assist with their manufacturing processes. It’s proving popular with hundreds of downloads.”
Looking ahead, the consortium envisions many thousands of these types of vehicles on the road by 2030.
Download a copy of the report here.
