Trw Automotive Safety Systems Gmbh

Helga Heist

Martin Kreuzer

Guido Hirzmann

Alexander Lammers

Hans-Jürgen Bossler

A device for detecting steering wheel contact comprises at least a first electrode () which is provided in a steering wheel () and which forms, together with a human body acting as a second electrode and a dielectric situated therebetween, at least one sensor capacitor (). The device also comprises an evaluation circuit () having a reference capacitor () of known capacitance which can be connected parallel to the sensor capacitor (), a direct current voltage source () which can be connected to the reference capacitor (), and a measuring device for measuring the voltage at the reference capacitor (). A method for detecting steering wheel contact using such a device comprises the following successive steps: charging the reference capacitor () by applying a known reference voltage, or charging the reference capacitor () and subsequently measuring a first voltage at the reference capacitor (); connecting, in parallel, the sensor capacitor () to the reference capacitor () so that a portion of the charge of the reference capacitor () is transmitted to the sensor capacitor (); measuring a second voltage at the reference capacitor (); end determining the capacitance of the sensor capacitor () from the known capacitance of the reference capacitor (), the reference voltage or the first voltage and the second voltage.

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Laufach, Germany

Helga Heist