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Current Events/News: Advantage Online: 2004 Archives

ADVANCEMENTS IN PASSIVE RESTRAINTS

Decision-Making Systems

As early as 1988, passive restraint systems began transforming from a “to deploy or not to deploy” situation, to a smarter system that decides if the seat belt pre-tensioner and/or airbag should be deployed. This decision is based on whether or not the occupants have their seat belts buckled.

In 1994, BMW began using dual-stage airbags. A dual-stage airbag contains a high and low power charge. This type of system is capable of making more decisions based on received crash criteria. The restraint system electronic control module (ECM) determines how many stages and at what sequence the airbags should be deployed. On these systems, during a collision, the restraints system ECM determines which seat belts are in use, (see Figure 1) and how quickly the vehicle is decelerating. These inputs allow the ECM to determine if an airbag should be deployed, which airbag or airbags should be deployed, how many stages should deploy, and in what sequence.

Here are examples of deployment scenarios with two different collision thresholds. In these examples, there are two occupants in the front seats. The vehicle has two dual-stage front airbags and front seat belt pre-tensioners.

1st Threshold (minor impact), and:

• both seat belts are buckled, both seat belt pre-tensioners deploy, and no airbags deploy.
• one seat belt is unbuckled, only that occupant’s airbag deploys, and the buckled seat belt pre-tensioner deploys.
• neither of the seat belts are buckled, both airbags deploy, and neither of the seat belt pre-tensioners deploy. Depending on the system, and the vehicle maker’s designed parameters, one or both stages of the airbags may deploy.

2nd Threshold (severe impact), and:

• both seat belts are buckled, both seat belt pre-tensioners and both airbags deploy. If the system uses dual-stage airbags, the stages may deploy simultaneously, or be staggered to maintain longer airbag inflation.
• neither seat belt is buckled, both airbags deploy, but not the seat-belt tensioners. If the system uses dual-stage airbags, the stages may deploy simultaneously, or be staggered to maintain longer airbag inflation.

If a passive restraint system part does not deploy, ALWAYS read the system description and operation for the circuit, before condemning a part as faulty.

Identifying A Passenger

As early as 1994, BMW was using a passive restraint system that could identify if someone was in the front passenger seat. This system is called occupant recognition (OR). If no occupant is in the front seat, the passenger airbag will not deploy.

Classifying The Passenger

Along with the operation of systems that monitor seat belt use for determining airbag deployment, an occupant classification system (OCS) also determines airbag deployment by the:

• weight of the occupant in the front passenger seat. This is determined by either a silicone-filled bladder (see Figure 2) or strain gauges (see Figure 3).
• stress on the seat belt.
• proximity of the passenger to the airbag. This is either determined with a seat position sensor or ultrasonic sensors.

As an example, DaimlerChrysler categorizes occupants in three groups depending on weight. When a weight is detected on the front passenger seat approximately equivalent to a:

• rear facing seat, less than 17 kg (37 lb), the OCS is designed to prevent deployment of the passenger airbag.
• six-year old child, 21.5 kg (47 lb), one production model vehicle uses a “low risk deployment” feature. This means that if specific crash criteria occurs, the least forceful airbag charge may be activated for an occupant between 17.5 kg (38 lb) and 45 kg (98 lb).
• fifth percentile adult, more than 45 kg (99 lb), the airbag may be allowed to function normally depending on the crash data received.

Conclusion

At this point in passive restraint system advancements, all collision industry professionals have the possibility of being faced with any of the systems mentioned in this article. Without knowing how the systems are designed to operate, and what, or who, was in each seat of the vehicle, it is impossible to know if a system was working as designed by the vehicle maker. This makes it especially important to have access to service manual information from the vehicle maker.

The different deployment scenarios that can occur with today’s advanced passive restraint systems is one of the subjects included in a new I-CAR program, “Advanced Restraint Systems (RES02),” which will be available soon.

Page Last Revised: Tuesday, May 2, 2006
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