The Case Study of Automotive Airbag Reliability

The case st udy of A ut omot i ve Ai r bag Reli abil it y

(Page 252)

(for comprehensive hints to solve the case study, refer to Page 217-220)
Q# 1: What is the role of the dual actuators in the mechanical air bag system? Describe the effect of having only one.
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The role of dual actuators is to activate the mechanism of the airbag.

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These dual actuators are the two shafts that move off the edge of spring-loaded firing pins where the pins then stab dual primers, igniting the enhancer.

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The actuators are designed in parallel in the system to provide better reliability. One of the actuator acts as a primary actuator and the second actuator acts as a redundancy or backup actuator in the mechanical air bag system in a case the system fails.

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The effect of having only one actuator eventually will reduce the reliability of the mechanical air bag system. (to prove this, we can calculate the reliability of the AMS Sensor Block Diagram in Exhibit 6.24 by: Firstly, by having two parallel actuators (Reliability = 99.97%) and the latter by having only one actuator (Reliability = 98.52%))

Q# 2: Compute the reliabilities of each system. What conclusions do the data suggest?
Reliability of All Mechanical Sensor (AMS) Air Bag System (see Exhibit 6.24)
For simplicity, two parallel actuators are computed as one actuator by applying
Eq. 6.3 on Page 219.
R=.985266
RAC = .999783

Actuator
=

Actuator

Actuator
R=.985266
The reliability for two parallel Actuators is
RAC = 1 - (1 - 0.985266)(1 - 0.985266)
RAC = 0.999783
Then calculate the reliability of AMS Air Bag System (RAMS) as
(0.999993)(0.999783)(0.999986)(0.999986)(0.999994)(0.999975)(0.999999)
RAMS = 0.999716  99.97% (see Equation 6.2 on Page 218)

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Reliability of Electromechanical Sensor System (EMS) Air Bag System
Similar idea is applied to calculate the reliability of EMS. First compute the reliability of the parallel system of Battery and