DETROIT -- Grammer AG has developed a headrest designed to reduce whiplash injuries in rear-end crashes.
The German supplier's redesigned electronic active head restraint system will debut on the 2007 Mercedes-Benz C class sold in Europe next year. It could be on other vehicles for the North American market that same model year, the company says.
Conventional headrests are mechanical. They are not designed to move during a rear-end collision.
And that's the problem, says Ervin Jahic, senior project manager at Grammer's U.S. office in Troy, Mich. Often the space between the headrest and the head is too great or the adjustment is too low to prevent an injury.
In a rear-end collision, the upper part of the passenger's body is held by the seat back. But inertia can force the head backward without any support unless it is stopped immediately by a headrest. The motion created by the rebounding body and the simultaneous backward movement of the head resembles a whiplash as the neck is forced into an S-shaped bend.
Jahic says Grammer's electromechanical headrests move forward toward the head within about 55 milliseconds. That's less time than it takes to blink an eye. By comparison, about 120 milliseconds are needed for an airbag to inflate.
Crash sensors trigger a module that controls the headrest.
"The complete mechanism is packaged inside the headrest," Jahic says. Grammer's module is small enough that it does not interfere with the headrest's design, he says. The headrest still can be adjusted up or down and can tilt for the occupant's comfort.
"Changes in seat structure are not required for this headrest, but the seat must be stiff enough to be used in combination with the active headrest," Jahic says.
Grammer's first-generation active headrest systems, which are not electrical, are on the BMW 5 and 7 series. But the latest design will comply with a National Highway Traffic Safety Administration rule approved last year - a rule requiring each front-seat restraint to be higher and closer to the back of the head. Adjustable restraints must lock into place.
The regulation takes effect in September 2008.