Published May 23, 2012
By Philippe Crowe
Volvo is becoming the first manufacturer to offer a pedestrian airbag. This feature will be offered on the newly-launched V40.
In China 25 percent of traffic fatalities are pedestrians. In Europe the figure is 14 percent and in the USA it’s 12 percent. A far larger number of struck pedestrians are injured. The most serious head injuries involving pedestrians and cars are caused by the hard structure under the hood, the windshield’s lower edge and the A-pillars.
How does it work?
Seven sensors embedded in the front of the car transmit signals to a control unit. When the car comes into contact with an object, the signals change. The control unit evaluates the signals and if it registers what it interprets as a human leg the pedestrian airbag is deployed.
Each of the hood hinges are equipped with pyrotechnical release mechanisms which, when the system is activated, pull out a pin and release the rear of the hood panel. At the same time, the airbag is activated and starts filling with gas. During the inflation sequence the airbag raises the hood; the hood lifts by four inches and stays in that raised position.
The added gap between the bonnet and the hard components in the engine compartment gives space for the hood to deform, creating a dampening effect when it is hit by a pedestrian.
“The airbag has two functions. Firstly, it raises the hood to create distance, and secondly it cushions the impact around the hard parts of the area near the windshield” explains Thomas Broberg, Senior Technical Advisor Safety for the Volvo Car Corporation.
In its inflated position, the airbag covers the entire windshield wiper recess, about one-third of the windshield and the lower part of the A-pillars. The entire sequence from activation of the system to full inflation takes a few hundredths of a second.
The system is active at speeds between 20 and 50 kph. 75 percent of all accidents involving pedestrians take place at up to 40 kph.
The airbag itself consists of a bag and a gas hybrid generator. Upon activation, the bag is filled with gas within a few milliseconds.
Here is a link to a video simulation: