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01/11/2007
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The concept of exterior airbags still appears to have some support, at least among developers of SUVs, writes Roger Bishop. The latest developments are aimed not only at reducing injuries to pedestrians but also at limiting side impact intrusion when an SUV is involved in accidents with passenger cars and other low-profile vehicles.
Pedestrians are two-and-a-half times more likely to die in an impact with an SUV than with a conventional passenger car, mostly as a result of these vehicles’ higher, more box-shaped front ends.
Another difference is the impact area. While most pedestrians killed by passenger cars perish when their heads hit the bonnet or windscreen area, the majority of severe injuries to pedestrians caused by SUVs occur when the bonnet’s leading edge hits the pedestrian’s chest and abdomen.
A ‘front edge airbag’ developed by Autoliv to address this problem is triggered by a pre-crash sensor (such as radar), and deploys a few milliseconds before impact. The system has been tested in both computer simulations and in real crash tests, involving crash dummies representing an average male and a very short female.
In simulations the airbag demonstrated an ability to pass EuroNCAP requirements and in full-scale testing the airbag decreased all critical injury values considerably. The largest reduction was for the abdomen of the male dummy. Here the injury risk was reduced from 99% to just 3%. The test velocity was 40km/h, said to be the average impact speed in fatal pedestrian accidents in the USA.
Autoliv’s new ‘bumper airbag’ deploys from beneath the bumper to protect the pedestrian’s legs. In tests, the violence to the lower legs of the pedestrian dummy was reduced by more than 50% to levels within the criteria set by EuroNCAP.
However, according to Autoliv, the most important application of the bag will probably be in crashes when there is a mismatch in vehicle heights,
especially when an SUV or other high-profile vehicle T-bones a passenger car. In these collisions, the front of the SUV typically hits above the sill and the energy-absorbing structure of the car, resulting in critical intrusions into the passenger compartment and, in some cases, collapse of the protective cage. The risk of death in such crashes is 27 to 48 times higher in a passenger car than in another SUV.
The 1.5m long tubular bumper airbag has been the subject of both computer simulation and real crash tests, mounted under the bumper of a Ford Explorer that was run into the side of a passenger car at 48km/h. Bag inflation started 80ms before impact, allowing the bag’s load-carrying structure to swing into position. Intrusions were significantly less at all measuring points, and at head level of occupants in the ‘target’ car the reduction was as much as 40%. In addition, side airbags in the car also have more time to deploy and inflate.
Sled and crash dummy tests currently being conducted indicate, says Autoliv, that the risk for rib fractures and other severe or fatal injuries to the upper body could be reduced by nearly 40%. So far only the upper body tests have been evaluated but the reduction at head level should be even greater.
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Author
Roger Bishop
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