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Shuttle-service ASES body with steel ring easy access side design and slide-together steel frame doors can meet side impact requirements. (SMDI)

Cutting weight seen as less important in automated and shared vehicles

After long demonstrating lightweighting with steel for contemporary passenger vehicles, the Steel Market Development Institute (SMDI) is slightly changing the tune for a future of Autonomous, Connected, Electric and Shared (ACES) vehicles. 

In a presentation to the International Motor Press Association, SMDI conceded that although weight on an isolated basis affects driving range and can’t be ignored, the total effect on the viability of ACES designs is not necessarily the same—and other qualities may be even much more important. And the bottom line on range versus cost is likely to be a wash, said SDMI vice president Dr. Jody Hall. 

When it comes to materials selection, weight can drop to second place when the vehicle’s environment changes, and for ACES vehicles, the primary concern is safety, particularly for vehicles where the occupants may not necessarily be seated in ideal positions.

Weight advisable for MaaS vehicles
Shuttle-service automated vehicles, for example, pose a variety of safety concerns. To accommodate easy entry of all types of passengers, a wide opening is desirable, and that raises vehicle B-pillar design concerns. The steel industry has been developing slide open/closed doors that when closed will latch into a bodyside ring, similar to an approach once used in utility vehicles, to meet regulatory side-impact requirements.

Inside (and without a driver) there is no practical way to ensure passengers are buckled up, so even if the vehicle is limited to low-speed operation, the extra strength of an all-steel structure improves its crashworthiness.

ACES vehicle operation relies on a wide range of inputs from external sources to its typically surface-mounted sensors and cameras, processed through electronic control units to onboard actuators. Although any input device that’s mounted on or close to an external surface has exposure to damage, SMDI said the greater strength of a steel vehicle made it a safer choice in an accident. 

Battery carriers scrutinized
SMDI also cited data from ArcelorMittal, a diversified steel company, in its presentation. Aluminum has become the material of choice for electric-vehicle (EV) battery packs in all premium models. However, SMDI pointed to ArcelorMittal’s steel-based battery-pack carrier that weighs within 10% of the aluminum design and for which it projects a per-vehicle saving of $120. The modular design of the tray includes upper and lower crossmembers, with the lower one integrated with the bottom cover. The liquid cooling system is centrally located in the structure; all components incorporate various high-strength steels.

The modest weight penalty of the steel battery carrier will be overcome in the upcoming generation of lithium-ion batteries, Ram Ilyer of ArcelorMittal R&D said. He compared an Audi e-tron with its 70% steel body and aluminum doors and other panels with a Jaguar I-Pace and its primarily aluminum construction: the two vehicles are somewhat different size and the Audi has a 95-kWh battery pack, vs. a 90-kWh pack for the IPace, so calculation adjustments were made for the difference in footprint. Assuming an aluminum price premium of $5 kg, the cost of going aluminum on the e-tron was projected to be $853, whereas adding battery capacity to overcome the extra weight of steel in the Audi, based on a 2020 price of $170 kWh, would be $850, effectively the same.

However, assuming continued declines in battery pricing, SMDI asserted that adding battery should soon be less costly than an aluminum-intensive vehicle design.

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