Rollover Detection

Rollover detection is provided by a rate of yaw sensor and two additional low-g sensors. The low-g sensors act in Y and Z directions.

There are different factors which can cause a car to overturn or roll over.

The most common causes are:

• The car hits a ramp (e.g. a crash barrier) on one side or the vehicle tilts due to the terrain. The car rotates about its longitudinal axis as a result of the high angular velocity.
• The car skids sideways off the road surface and its wheels become buried in soft soil. The kinetic energy could be sufficient to upend and overturn the car.
• The car skids sideways off the road into the curb and is upended.

The crucial factors which determine whether the car overturns are not just the angle of rotation but also the angular velocity or angular acceleration at which the car is set into the roll. All these vehicle movements can also occur after a front-end, side-on or rear-end crash.

The two Low-g sensors have a small measuring range of 0-2 g and can therefore detect small accelerations and decelerations with great accuracy.

For example, when the vehicle skids sideways off the road surface and buries itself with its wheels in soft ground.

The sensors provide a voltage as measured variable. This voltage is a measure for the acceleration and is converted directly into digital signals in the sensor. The digital values are sent to the crash safety module for evaluation. The crash safety module evaluates the signals from the two Low-g sensors and the rate of yaw sensor. The results are compared with the stored algorithm. If the processor detects that a rollover situation is imminent, the seat belt pretensioners and the head airbags are triggered.

The sensor cluster is connected via a four-wire lead. A current interface which transfers a special report is used so that for the five sensors, this saves on six leads. This interface is also used for the other airbag sensors, so that, here too, savings can be made on leads and thereby weight.