Impact Sensor: Description and Operation

The inflatable restraint forward discriminating sensor is used by the SDM in order to determine it a frontal crash requires deployment of the air bags. The sensor consists of the following components:
^ A sensing element
^ Normally open switch contacts
^ A diagnostic resistor

If the changes in vehicle speed are severe enough, the sensing element closes the switch contacts in order to cause deployment. The diagnostic resistor is connected in parallel with the switch contacts inside the sensor. The diagnostic resistor and the resistors in the SDM cause a voltage drop that allows the SDM to monitor the inflatable restraint forward discriminating sensor and the associated circuitry.




If the vehicle is in a frontal crash of sufficient force, the SDM allows current through the deployment loops. The current that passes through the initiator ignites the material in the inflator module (2). The gas from this reaction quickly inflates the air bag (1).




A shorting bar is placed on the connector of the inflatable restraint IP module (1) that connects to the SIR wiring harness. If the connector of the inflatable restraint IP module (1) is disconnected, the shorting bar shorts across the circuits of the inflatable restraint IP module (1). This prevents inadvertent deployment of the air bag during service to the module, to the instrument panel (2), or to the other components of the SIR system.