Active Head Restraint System (AKS)

Active Head Restraint System (AKS)




Another innovation of the E65/E66 is the Active Head Restraint System which is part of the driver and passenger multifunction seat (comfort seat).

No active head restraint is installed for the basic seat, as the fixed positioning between the backrest and head restraint means that the occupants head is always positioned near the head restraint.

In a rear-end collision, the occupants are accelerated along with the vehicle. The upper torso and pelvis of the occupants rest against the backrest and thus absorb this acceleration immediately.

The head, in contrast, is usually not in constant contact with the seat and therefore is slower to respond to the forces acting on the vehicle body. In the initial phase of the crash, the head remains in its original position. In relation to the body, which moves forwards, the head moves backwards.

It is only when the head makes contact with the head restraint that this relative movement between head and body is reduced and the head then is accelerated at the same rate as the body.

This pitching motion of the head, leads to cervical vertebrae injuries (whiplash). The danger of cervical vertebrae injuries is higher when there is a greater distance between the head and head restraint. The head restraints are intended to prevent, to the greatest possible extent, the dangerous pitching motion of the head.

In the case of the multifunction seat, the adjustability of the head restraint means that there is the possibility that the gap between the head restraint and head increases. In the event of a crash, the gap could be relatively large, leading to greater strain on the cervical vertebrae.

For this reason, the active head restraint was developed. In the event of a crash, this system reduces the gap between the head restraint and head and thus the rate of cervical vertebrae injuries.




The active head restraint system is located in the backrest of the multifunction seat. It consists of a support tube, which is fitted on bearings in the backrest. A retaining plate attaches the system firmly with the backrest.

The support tube serves as fixture for the head restraint, the adjustment mechanism of the head restraint, as well as the head restraint height adjustment.

The adjustment mechanism consists of a retaining plate and a sliding element. The sliding element is a moveable part connected to the gate located on the support tube. The retaining plate is firmly attached to the backrest, The generator is located between the retaining plate and the sliding element.




The generator consists of a casing, plunger, ignition stage and connection. It is attached to the retaining plate and the sliding element by spring clips.

In the event of a crash, the ignition stage is activated, the solid fuel burns and the gas produced forces out the push rod. The push rod moves out and shifts the sliding element.

The support tube is pivoted forwards because of the slanted, elongated holes in the support tube which the sliding element rides in.

This means that the head restraint attached to the support tube is also moved in the direction of travel. The adjustment range of the headrest is approx.9 degrees.

Depending on the vertical adjustment of the head restraint at the time, different adjusting distances can result. The adjustment of the head restraint, measured on the cushion, is approx.40 mm when the head restraint is retracted (all the way down).

When the head restraint is fully extended (all the way up), the adjustment is approx.60 mm.




If the Active Head restraint has been triggered in a crash, only the gas generator needs to be replaced to return the system to normal function.