Autoliv has recently presented a new system to protect pedestrians when struck by cars. The new system could significantly reduce the risk for serious and fatal head injuries.
In Europe over 7,000 pedestrians are killed annually when struck by cars and head injuries account for the vast majority of fatalities.
In Autoliv’s new pedestrian protection system, sensors in the front bumper of the car send signals to two actuators, which lift the rear part of the bonnet.
This is said to give the bonnet a sufficient deformation range to ease the impact of the pedestrian’s head, which is the area of the body Autoliv has focussed it’s research on.
‘Most pedestrian fatalities in car collisions are sustained when the head violently hits the bonnet or the lower part of the windshield,’ said Yngve Haland, Autoliv’s Research Director and Professor at the Chalmers University of Technology in Gothenburg. ‘Our current technology allows us to develop an active system such as lifting the bonnet.’
‘Collision protection systems for pedestrians have been studied for over fifteen years. However, few proposed solutions are both effective and economical,’ added Haland. ‘Our solution has the advantage, not to require any changes of the car design that could for instance increase fuel consumption.’
The idea of lifting the bonnet is common knowledge, but to do this in time before the head hits the bonnet has proved to be difficult. Developing a sensor that can distinguish between a human leg and, for instance, a lamp-post has been even more difficult.
Autoliv’s patented solution employs compressed steel bellows, which are empty until a pedestrian is struck, then are inflated by gas generators. Two bellows – one on each side of the bonnet – are inflated to lift the bonnet about 10 cm.
This is done in 60-70 milliseconds after the bumper has hit the pedestrian’s leg. A typical head-to-bonnet impact at 40 km/h occurs at about 150 milliseconds after the leg is first hit.
In laboratory tests, the system is said to have significantly reduced the critical injury value HIC (Head Injury Criterion) to levels consistently below standards proposed by the European Union.
Of all car-pedestrian accidents 95 per cent occur at less than 60 km/h impact speed. The average impact speed is about 40 km/h. The proposed EU directives are based on this impact speed.