Safely on the road in electric cars

9/22/2014

Efficient, subcompact vehicles with electric drives provide an excellent opportunity to push forward electromobility. However, traffic experts warn that the current safety standards of the L7E vehicle class ("quad class") are not sufficient for wide-scale deployment in traffic. Researchers of the Visio.M consortium’s "Safety" subproject have accepted this challenge and are now demonstrating how even light and efficient electric vehicles can achieve an acceptable level of safety.

Visio.M's rigid passenger compartment made of carbon fiber reinforced plastic provides effective protection - Photo: IAV GmbH

Systematic light-weight construction is a decisive component of efficient electric vehicles. Yet, during Euro NACP testing light-weight L7E class vehicles (max. empty weight of 400 kg) show substantial deficits in some areas. Because the requirements for the so-called quad class are low, safety experts are calling for more effective passenger protection in light electric vehicles should they populate roads in larger numbers.

Regardless of their reduced size, compact vehicles must provide passengers with a safe compartment, especially in collisions with heavier vehicles. The Visio.M achieves this through a rigid passenger compartment made of carbon fiber reinforced plastic. The deformation zones in the front and rear sections, as well as the roof structure, are made of high-strength aluminum profiles.

Foresightful sensor systems

The great rigidity of the passenger compartment and the unavoidably smaller chassis deformation length translate to high forces stressing passengers during an accident. Viso.M counteracts this with an integrated safety concept based on the sophisticated recognition of surrounding traffic via radar and camera sensors.

Thanks to its 360° detection of the immediate vehicle surroundings, Visio.M recognizes critical driving situations early on. This information is used not only for driver assistance and warnings. When it senses an imminent collision, it activates the integrated passenger protection system even before the actual crash occurs.

A key component of this strategy is the integration of structural airbags: heavy duty pressure hoses mounted in the bumpers and side panels. Fractions of a second prior to impact a gas generator fills the pressure hoses. Thus the exterior panels are pressed outwards, placing themselves between the outer skin and chassis as an additional absorption layer.

Effective passenger protection

The forces stressing the passengers are controlled by adaptive seat-belt tensioners and force limiting systems. An additional two-point safety belt inside the vehicle holds passengers firmly in their seats. When the vehicle detects an unavoidable side collision, the seat on the impact side is pulled towards the middle of the car, a split second before the crash. This moves the passenger out of the immediate danger zone. Furthermore the pre-acceleration also reduces the impact force on the passenger and increases the effectiveness of the side airbag. An airbag between the seats of driver and passenger alleviates any contact between the passengers.

In countless computer simulations, the researchers of the Visio.M "Safety" sub-project, which includes the firms Autoliv, Daimler and IAV, as well as TU München, tested possible accident scenarios and verified their calculations in full-scale crash tests. "Our results show that the innovative solutions of the Visio.M realistically resolve the conflict between extreme light-weight construction and an acceptable level of safety," says Thomas Unselt (Daimler AG), spokesman of the “Safety” project group. "Our concept considers significant requirements of the NCAP Protocol for vehicles of the 3.5 ton M1 class and, thus, goes well beyond the legal requirements for L7e vehicles."

Participants in the Visio.M consortium are, in addition to the automotive companies BMW AG (lead manager) and Daimler AG, the Technische Universität München as a scientific partner, and Autoliv BV & Co. KG, the Federal Highway Research Institute (BAST), Continental Automotive GmbH, E.ON AG, Finepower GmbH, Hyve AG, IAV GmbH, InnoZ GmbH, Intermap Technologies GmbH, LION Smart GmbH, Amtek Tekfor Holding GmbH, Siemens AG, Texas Instruments Germany GmbH and TÜV SÜD AG as industrial partners. The project is funded under the priority program "Key Technologies for Electric Mobility – STROM" of the Federal Ministry for Education and Research (BMBF).

Contact:

Prof. Dr.-Ing. Markus Lienkamp
Technische Universität München
Chair for Automotive Technology
Boltzmannstr. 15, 85748 Garching, Germany
Tel.: +49 89 289 15345 – E-mail

Technical University of Munich

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