Six airbags are now standard in almost all cars in Europe, and eight is not uncommon. An additional airbag could soon be added. And one for the feet. ZF Lifetec has developed the Active Heel Airbag.
The knee airbag is already in widespread use. It complements the frontal restraint system consisting of the seat belt and frontal airbag and can further improve occupant protection by transferring some of the restraint energy into the car via the knees and thighs. To achieve this, it is necessary to ensure that the feet remain securely positioned in the footwell during a crash.
If, in the future, the seats are allowed to be moved further back during the journey to so-called comfort positions, the contact surfaces for the feet may be too far away. In the event of an accident, the resulting uncontrolled movement of the legs can increase the risk of injuries to the lower extremities. Although many of these injuries are not life-threatening, they can result in long-term impairment of the musculoskeletal system of the driver and front passenger.
Supplement to the knee airbag
This is why ZF Lifetec has developed the Active Heel Airbag, which can help to ensure a stable heel impact point even in a relaxed seating position with the seats pushed back.
Occupant safety depends on a number of factors, including the position of the legs, knees and feet. In conventional seating positions, the car floor provides sufficient support for the feet of front seat occupants, ensuring a stable heel strike point that allows a controlled knee curve.
This also ensures that the knee joint can enter the knee airbag at the most favourable angle, thanks to the secure support of the heel in the footwell. This allows a large proportion of the crash energy to be absorbed by the car's structure via the thigh - the strongest bone in the human body.
However, crash tests have shown that an additional heel impact point must be created as soon as the occupant moves the seat back to a more comfortable position, as this increases the distance between the heel and the impact point and the coupling to the floor of the footwell is no longer optimal.
The comfort position challenge
"If the heel contact point is missing, the knees can hardly be effectively immersed in the airbag and the knee airbag does not achieve its full effect," explains Harald Lutz, Head of Development at ZF Lifetec. The knee joints can no longer support themselves in the intended position, resulting in uncontrolled movement of the legs. Although the risk of fatal injury is low in this case, without the Active Heel Airbag there is a high probability of serious leg and foot injuries. "The Active Heel Airbag helps to ensure an adequate heel impact point even in more comfortable seating positions," adds Lutz.
The challenge on the driver's side
The Active Heel Airbag can also be used for comfort positions on the driver's side. For future applications, it is therefore possible to activate the Active Heel Airbag via a comfort position button or camera-based interior monitoring on the driver's side, for example during assisted driving.
By embedding the pedals, the Active Heel Airbag creates a uniform contact surface for the heel in the event of an accident. This further reduces the risk of injury caused by twisting of the feet when hitting edges such as the brake pedal.
Space-saving technology
The Active Heel Airbag can be integrated directly into the footwell without taking up any additional space. In the event of a crash, the airbag inflates under the vehicle's floor carpet, providing the necessary heel stability. The Active Heel Airbag can be adapted to almost any vehicle model worldwide. The Active Heel Airbag will be available from 2028 for vehicle manufacturers who wish to offer their passengers seats with extended comfort positions.
