Abstract: An improved distributed architecture SIR system wherein the idle voltage of the power and communications bus is regulated by a fault tolerant power supply circuit, and portions of the bus coupled to devices located in a crush zone of the vehicle may be de-coupled from other portions of the bus in the event of a short circuit across the wires of that portion of the bus. The power and communications bus comprises two wires (signal and ground) and the bus ground wire is weakly biased to a reference voltage. A boost power supply referenced to the bus ground establishes the nominal voltage of the signal wire, and supplies charging current over the signal wire to the energy reserve circuits of various devices coupled to the bus. The power supply is transformer-isolated from the bus, and the feedback circuitry for controlling the operation of the power supply senses the bus voltage as coupled through the transformer.

Abstract: A distributed architecture SIR system having remote sensor and initiator driver modules communicating over a common bus utilizes an address communication method which permits the communication of information to multiple remote modules at the same time, thereby minimizing the number of messages that must be transmitted across the bus to cause a given action to occur. According to the method, each remote initiator driver module is assigned three different ID codes: a node ID code, a deployment event ID code and an occupant zone ID code. The node ID code is unique to the module, and is used for the transmission of information (such as diagnostic state) specific to that module. The deployment ID code identifies multiple remote initiator modules associated with restraint devices which will ordinarily be deployed concurrently in a given type of crash event, and is used for the transmission of deployment commands to such modules.

Abstract: A deployment control method for distributed architecture SIR system provides improved fault tolerance and ensures that signals generated by various remote sensor modules are properly considered in determining whether to deploy restraint devices. The deployment control method establishes a succession of states, wherein entry into each state is conditioned upon the achievement of predetermined criteria, and deployment of a respective restraint device is conditioned upon the successive achievement of each state. The states include an inhibit state, an enabled state, an armed state and a deployment initiated state. The predetermined criteria include correct occupant position, collision verification or safing, and collision severity. Deployment can only be initiated when the initiator module has been advised that all three criteria have been met within a given time constraint.

Abstract: An SIR has an AND gate for selectively passing a deployment signal from a deployment circuit to a firing circuit. An arming circuit includes a logic circuit containing a small normally closed arming sensor which disables the AND gate until a prescribed acceleration level occurs to open the arming sensor. A pulse stretcher ensures that if the sensor opens only briefly, the AND gate will remain enabled long enough to complete deployment. The arming sensor comprises a plastic housing with a cylindrical cavity, terminals closing opposite ends of the cavity, and a spring biased mass in the cavity which electrically connects the terminals until an acceleration moves the mass to break the connection.

Abstract: A firing circuit for multiple vehicle passenger restraint initiators, wherein initiators located in proximity to each other are paired in first and second parallel connected firing loops terminated by first and second firing circuit nodes. The first firing loop includes one of the initiators and a first diode poled to conduct current from the first node to the second node, and the second firing loop includes the other initiator and a second diode poled to conduct current in the opposite direction, that is, from the second node to the first node. A switching circuit, such as a four-element bridge couples each pair of firing loops to a source of DC so that the source voltage can be applied to the firing loop nodes in either polarity, depending on whether the switching circuit receives a first firing signal or a second firing signal.

Abstract: The firing loop of a SIR system has a firing element, a capacitor for passing AC pulses to the element and an inductance which varies according to application. A current sensor monitors each pulse and detects a threshold crossing on the trailing side of the pulse, and a toggle circuit operates a switch arrangement to terminate the pulse and initiate the next pulse of opposite polarity. This current feedback circuit varies the pulse frequency according to the loop inductance but the RMS loop current is independent of inductance.