A New Micromechanical Pressure Sensor for Automotive Airbag Applications
Automotive restraint systems today are more and more using pressure sensors in order to early and safely detect side crashes. A reliable, precise and fast measurement of the air pressure is the key precondition for an optimized system performance.
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A New Micromechanical Pressure Sensor for Automotive Airbag Applications
B. Adam, T. Brandt, R. Henn, S. Reiss, M. Lang, Ch. Ohl Robert Bosch GmbH
Abstract Automotive restraint systems today are more and more using pressure sensors in order to early and safely detect side crashes. A reliable, precise and fast measurement of the air pressure is the key precondition for an optimized system performance. We present a new generation of Bosch pressure sensors called PPS2 (Peripheral Pressure Sensor) that is specifically designed for airbag system application. The key component of the sensor is a pressure sensor module (SMD187) that integrates a micromechanical membrane, an ASIC with band-pass filter, trimming, and signal processing as well as the digital interface. The micromechanical part is realized using the new pressure sensor technology developed by Bosch named APSM (Advanced Porous Silicon Membrane). APSM purely bases on surface micromechanical process steps and turns out to be very robust monocrystalline Silicon membranes. The sensor provides a filtered and normalized differential pressure signal P/P0 to the airbag ECU using the well-established PSI5 standard current interface. The pressure range of the sensor allows to run the system at altitudes up to 4000 m above sea level. The normalized differential pressure signal is transferred within a range of -5 to +15% of the ambient pressure. PPS2 allows easy application and system setup, offers high system flexibility and provides a reliable, precise and fast pressure signal to the airbag system.
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Components and Generic Sensor Technologies
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Introduction
In 1996, the first airbag pressure sensor for detection of side crashes was introduced. Due to increased performance requirements in regards to side crash protection pressure sensors have become widely utilized. Today, pressure sensors are common practice for fast and robust detection of side crashes in middle and upper class vehicles. Mostly, the performance of airbag systems gets optimized by combining pressure sensors with acceleration sensors. By using systems with suitable combinations of pressure and acceleration sensors the system firetimes and the robustness against misuses can often be improved compared with systems that are purely based on acceleration sensors. The crash detection bases on measuring the increased pressure inside the door cavity due to the deformation of the door during an impact where the sidedoor gets hit. Pressure signals used for firing decisions often allow a faster and safer distinction of different kinds of crashes. The signals are directly correlated to the deformation of the door and thus to the crashseverity. The sensor is mounted inside the side door cavity. It can be placed either in the dry-room or in the wet-room area. However, the sensor always senses the pressure inside the outer wet-room cavity and thus must always be connected to the wet-room area of the side door. The second generation pressure sensor PPS2 by Bosch provides a pressure sensor solution specifi
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