Introduction:
In a rear-end collision, the occupant is pressed into the seat and the head moves relative to the upper body with a very rapid motion backwards and forwards. Because of the stretching of the neck muscles, this can result in permanent injury: whiplash. In such a collision, the active headrest provides protection by moving forward. The occupant’s head is supported so that the neck does not make an excessively large movement.
The following image shows the situation with an active headrest (above) and without an active headrest (below).
Mechanical active headrest:
A seat with a mechanical active headrest contains a pressure plate that is pushed backwards by the body weight. Via a lever mechanism, the headrest is moved upwards and forwards. The movement of the headrest supports the person’s head and slows its motion.
Immediately after the collision, the pressure plate and the headrest automatically move back to their original position.
Electric active headrest:
In this system, the moving mechanism is integrated only in the headrest. The headrest consists of two elements that are pushed apart during a collision by an electromagnetic actuator. The airbag control unit controls the actuator. After activation, springs between the two elements push the cushion towards the person’s head and neck. The headrest itself does not move during a collision. After activation, the headrest can often be reset using special tools and diagnostic equipment. In other cases, it is necessary to replace the actuator.
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