Continental's new generation of sensors measure structure-borne sound during a crash and trigger the airbag safety systems at the optimum moment

Continental, the international auto-motive supplier, has developed a Crash Impact Sound Sensing (CISS) system which controls airbag ignition so precisely that, in the event of an accident, the vehicle occupants are provided with maximum protection. The characteristic structure-borne sound caused by an impact allows CISS to detect both the accident and its severity and to distinguish even more quickly and more reliably between different crash situations. Consequently, even in the case of serious accidents, the decision to trigger ignition of the restraint systems can be taken more quickly, providing vehicle occupants with the maximum reliable protection while suffering the least physical stress.

Measuring structure-borne sound: CISS detects an accident's severity earlier

In the event of a serious accident, the airbag safety system must decide what needs to happen within fractions of a second; in the case of a frontal crash, it has between 10 and 40 milliseconds to decide. Is the impact so severe that the airbags really have to be triggered? Or are the airbags not needed at all; and will the other passive safety elements, such as the crumple zone and seat belt, suffice? Alternatively, is the impact so violent that the priming charge which inflates the airbags needs to be activated at full force? Or is there time for a two-stage initiation?

The advantage of a two-stage initiation is that the occupants suffer less physical stress. These decisions are taken by sensors which measure the vehicle's rate of deceleration. The data obtained is analyzed in the central airbag control unit (ACU). The aim must be to make the sensors so sensitive that the deformation of the vehicle is registered as an additional important accident parameter. And it is precisely this which CISS makes possible since the highly-responsive structure-borne sound sensor covers virtually the whole front end of the vehicle and so, regardless of how directly the vehicle collides with an obstacle, it generates quantities of data extremely rapidly for evaluating the severity of the accident.

When the vehicle collides with an obstacle, the CISS system registers the speed at which the body shell distorts and the speed and strength at which the structure-borne sound waves are transmitted. A complex signal evaluation system, which uses specially developed algorithms to analyze and assess the accident, takes the ultimate decision as to whether the airbags should be initiated and with

what force. An additional plus : the CISS technology can be integrated within the airbag control unit - a cost benefit together with significantly improved performance.

clipSat: rapid reaction to a side crash

Initiating side and head airbags in the event of a side crash demands considerably more rapid reaction times than for the front airbags. In such cases, the system must have the life-saving airbags inflated within 5 to 10 milliseconds.

In a side crash, there is no large crumple zone to protect the driver or front-seat passenger as is the case in a frontal impact; there is only a gap of a few centimeters between door, B-pillar and occupant. More than ten vehicle manufacturers now install Continental's pressure satellite sensor which covers a large area of the vehicle, reacts rapidly and is not susceptible to being triggered in error.

If a side impact occurs, the sensor registers the change in the door tension caused by its deformation. The data obtained is analyzed by software in the airbag control unit, followed by the decision as to whether to initiate the side airbags. Because the sensor measures the whole of the side door and is not reliant on the deceleration rates measured in the fixed vehicle structures in a crash, it also achieves excellent results in the event of a pole crash where the vehicle collides with a narrow obstacle or in a collision with SUV vehicles where the main impact point is usually higher than for most other vehicles.

The latest generation of pressure satellites, called clipSat, also offer time and cost advantages during assembly. The clipSat pressure satellite can be simply clipped onto the inner door panel without the use of tools or other fastenings.

Modular design airbag control units: efficient, flexible and inexpensive

The SPEED (Safety Platform for Efficient & Economical Design) airbag control unit, developed by Chassis & Safety Division of Continental has a three-stage modular design which can be easily adapted to the requirements of different vehicle producers and markets. Essential functionalities, such as actuating the front and side airbags, are covered by SPEED's basic S variant, while the M variant includes multi-stage front and side airbags as standard. Other features, such as rollover protection which detects that the vehicle is about to overturn, can also be integrated as an enhancement. And, lastly, SPEED L includes front and side impact plus rollover detection as standard equipment. Whereas the S version can initiate up to 14 detonators in airbags or seat belt tensioners, the L version has interfaces for up to 30 actuators. Consequently, SPEED offers great flexibility, including the option of precisely tailoring the airbag control unit to the manufacturer's requirements, while largely benefiting from an identically engineered design, standard interfaces and mass-produced components.