Restraints and Safety Systems: Description and Operation
Deployment Loop and Sensing and Diagnostic ModuleThe deployment loop and Sensing and Diagnostic Module (SDM) are the two main portions of the Supplemental Restraint System (SRS). The deployment loop portion supplies current through the SRS modules, which are used to deploy the air bags in the event of a front end collision of sufficient force up to 30 ° off vehicle centerline.
Fig. 2 Deployment Loop Diagram:
The deployment loop consists of the arming sensor, SRS coil, inflator modules and discriminating sensors, Fig. 2. The arming sensor switches power to the inflator modules on the deployment loop high side.
Either of the discriminating sensors may provide ground to the inflator modules on the deployment loop low side. The modules will only be supplied sufficient current to deploy when the arming sensor and at least one of the two discriminating sensors closes simultaneously for three milliseconds or more.
The Sensing and Diagnostic Module (SDM) contains a 24 Volt Loop Reserve (24 VLR) and a sensing device to convert vehicle velocity changes to electrical signals. These are processed by the SDM and compared to a value stored in memory. If the generated signal exceeds the stored value, the SDM sends current flow to the air bags and deploys them.