Crash detectors determines collision severity

September 26, 2012 // By Christoph Hammerschmidt
Bosch has introduced the next generation of peripheral acceleration sensors for passenger protection systems in vehicles - the fifth one since 1996. Key features include a wide measurement range of between ±120 g and ±480 g and the choice of communication via the SPI or the PSI5-V1.3 interface.

Peripheral sensors are located at the outermost points of a vehicle's engine compartment, at the sides, or at the rear, thus enabling them to recognize a collision during an early stage. However, the new fifth-generation models can do more than simply register a crash. In just a few milliseconds, they send all the data needed by the airbag control unit to determine with certainty whether a collision is minor or serious. The control unit checks the plausibility of the incoming sensor data before deciding which vehicle restraint systems (e.g. front, head or side airbag and seat-belt pretensioners) to activate.

Apart from their measurement ranges, the two new sensors are of virtually identical design. The measurement range of the SMA58x can be switched from ±120 g to ±240 g and is designed for integration into the peripheral side collision sensors. The SMA59x, with its measurement range twice as wide as the SMA58x, is specially designed for front collisions. Both sensors measure along the Y axis. The 10-bit measured-value resolution and measurement range limit values are used to calculate sensitivity values of between 1 LSB/g and 4 LSB/g.

Thanks to the PSI5-V.1.3 bus interface, the sensors can be easily integrated into the car's electronic environment, provided the airbag control unit also features a Peripheral Sensor Interface 5. Up to four bus users can then be operated in parallel or in series. To ensure proper function of the data bus under the difficult conditions of a crash, the new acceleration sensors feature an IDATA pin, which is used to select filters or attenuators with customer-specific dimensions. This wiring is integrated into the package of the peripheral sensors along with the sensor chip.

Bosch engineers have equipped the SMA58x and the SMA59x with an ultra-effective offset controller, which automatically makes both slow and fast offset adjustments. As a result, the sensors are very resilient to physical disturbances such as vibrations or significant fluctuations in