ISIS headrests

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 at an early stage. In this case, the head is the most unresponsive part of the occupants: in the initial phase of the crash, the head remains in its initial position. Viewed in relation to the body, which moves forwards, the head moves backwards. It is only when the head makes contact with the headrest that this relative movement between head and body is restricted: the head is accelerated to the same extent as the body.

This pitching motion of the head leads to cervical vertebrae injuries. The danger of cervical vertebrae injuries is higher the greater the distance between the head and headrest in the initial position. The headrests prevent the dangerous pitching motion of the head to the greatest possible extent.

• Electrically extendable rear headrests: the electrically extendable rear headrests support the head to prevent ”whiplash” of the cervical vertebrae in the event of a crash. This can prevent the 'whiplash' syndrome (painful stretching of the neck muscles, tendons and nerves).
  

Brief description of components

Rear headrests

Electrically extendable rear headrests are fitted in the special equipment

• special equipment ”side airbag for rear seat passengers, incl. head airbag and electrically extendable outer headrests” (with SSH, satellite, rear seat)
  
• special equipment ”rear Comfort seats, with electric adjustment”.
  

The rear headrests are not secured in the backrest but firmly mounted on the cross member of the rear shelf. As they are thus solidly attached, active movement of the headrests as in the case of the front seats is not technically feasible.

Control units for the electric rear headrests: the activation of the electric rear headrests is integrated in the SSH (satellite, rear seat). If the special equipment ”rear Comfort seats, with electric adjustment” is fitted, the seat module controls the headrests.

Extending the headrests: the headrest on each side is extended when

• the seat occupancy recognition detects occupancy and
  
• terminal R is ON
  

Retracting the headrests: The headrests are returned to their home position when the headrest is extended and

• the seat occupancy recognition detects an empty seat or
  
• terminal R is switched off.
  

Undervoltage cutout The activation of the headrest motors is time-controlled. The time can be coded. At vehicle voltage less than 8.5 V, there is no activation of the headrest motors. However, the requirement remains and is performed when the vehicle voltage rises above 9 V.

Fault messages: the motor control sends a fault signal in the case of overload and interruption.

Seat occupancy recognition, rear left and rear right

The seat occupancy recognition, rear right and left, is fitted with the special equipment ”side airbag for rear seat passengers, incl. head airbag and electrically extendable outer headrests”.

The signals of the link and right seat occupancy recognition are read in by the SSH (satellite, rear seat).

Control units

The following control units are involved in the message transmission for the battery headrests:

• Seat module for headrest adjustment rear left and rear right with special equipment ”rear Comfort seats, with electric adjustment”.
  
• SIM (Safety Information Module)
  
• SSFA (satellite, driver's seat)
  
• SSBF (satellite, passenger's seat)
  
• SSH (satellite, rear seat)
  

Service functions

Note on safety

All work on the priming caps of the active headrests and on the electric motors of the rear seat headrests must only be conducted with the battery disconnected.