The Hood That Explodes For Safety

by Illustration: Kate Francis; Image: Courtesy Ford Motor Company Illustration: Kate Francis; Image: Courtesy Ford Motor Company

It sounds like something out of a Bond flick: a car with a hood that´s launched open by a pair of explosive charges. But Jaguar´s Pedestrian Deployable Bonnet System (PDBS) isn´t intended to thwart bad guys. Its purpose is to soften the impact on the unfortunate soul who gets hit by the European version of the 2007 Jaguar XK. PDBS is Jaguar´s response to new European Union legislation that requires automobiles to be gentler on pedestrians in the event of a collision (exploding hoods have not been greenlighted in the U.S.).

On impact, sensors in the bumper gauge an object´s size and weight. So hitting a trash can won´t trigger the system, but if a person is hit, two pyrotechnic charges at the base of the windshield inflate airbag-like posts, popping the hood. All this happens in 30 milliseconds-less time than it takes to look both ways.

How It Works:

1. Our hapless pedestrian steps into the path of an oncoming Jaguar XK.
2. The XK´s nosecone, carefully sculpted to tip a pedestrian onto the car´s hood without breaking the leg at the knee, makes contact.
3. As the impact occurs, a sensor array ascertains the size, shape and mass of an object. If the readings indicate that a person has been struck, the car triggers the PDBS system.
4. Two pyrotechnic actuators explode with roughly the power of 12-gauge shotguns. The blasts inflate tiny cylinder-shaped airbags enclosed in strong yet flexible tubes of braided polyester filament.
5. The tubular posts punch upward and raise the 40-pound aluminum hood about 2.5 inches in a scant 30 milliseconds, creating a crumple space above the engine.
6. The pedestrian´s head and upper body make contact with the hood, which collapses in a controlled manner, thanks to a hexagonally-stamped endoskeleton.
7. The pyrotechnic posts, like passenger-compartment airbags, immediately vent their gases and deflate, lowering the hood and restoring the driver´s forward visibility.

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