 | ||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
|
Servicing AirbagsPosted 12/16/2002By Keith Reinhardt
As automobiles have evolved, so has occupant safety technology. To the large majority of the motoring public the achievements of this technology are not obvious until a vehicle "crash" has occurred. In contrast, it is imperative that automotive service technicians not wait for a crash, but instead maintain a constant awareness of any changes in occupant safety technology. To meet new government regulations regarding occupant safety, automobile manufacturers - through the implementation of "dual stage airbags" - are modifying the operation of the Supplemental Inflatable Restraints (SIR) system. Consequently, to the service technician, dual-stage airbags necessitate knowledge of new system components to accurately and safely service today's SIR systems. Dual-Stage Inflator Modules Of all the components found on today's SIR systems, the inflator module, which contains the airbag, is the most visible. The inflator module's sole purpose is to protect the vehicle's occupants from harm during a collision by providing an energy-absorbing cushion at the proper moment in time. As technology has advanced, so have inflator module designs. Presently, auto manufacturers use a combination of driver, passenger, and side inflator modules to protect occupants. Beginning in 2001, auto manufacturers began equipping some of their new models with "dual-stage" inflator modules. If equipped, these new-style inflator modules are implemented in the steering wheel and instrument panel (IP) inflator modules only. To vary the amount of energy available to deploy the airbag, inflator modules of the dual-stage type can set in motion either two or three stages of airbag deployment strategies. Unlike earlier airbag inflator modules that use only one squib igniter, dual-stage inflator modules incorporate two squib igniters that control the temperature and thus pressure applied to a gas chamber. In general, a minor crash impact activates one squib igniter, resulting in slower airbag deployment with less initial force; whereas a severe impact activates both squib igniters for full and immediate airbag deployment. While some auto manufacturers facilitate this type of two-stage deployment, DaimlerChrysler AG uses a "multi-stage" of airbag deployments that still functions with only two squib igniters. An additional strategy for an intermediate-level impact is made possible by separating the activation of the two squib igniters by a few milliseconds. This intermediate stage of deployment is accomplished through control module software strategies. Although these inflator modules have three stages of airbag deployment possible, they are still dual-stage inflator modules given that they function with only two squib igniters. Dual-Stage Inflator Module Service Precautions
Sensors To properly deploy dual-stage airbags, SIR control modules require new innovative sensors and deployment strategies. For both driver and passenger airbag deployment strategies, SIR control modules rely upon a combination of sensor inputs including crash severity and seat belt switch status (buckled or unbuckled). Additionally, to complement driver-side sensor inputs, some vehicle applications include a driver's seat track position sensor. Likewise, an "Occupant Classification Sensor" may be used to ensure proper passenger airbag deployment or passive deactivation.
Seat belt sensors are located in the driver and passenger belt buckles or retractors. Several auto manufacturers simply use a mechanical switch, while others use Hall-effect sensors. These switches indicate safety belt status to the control module. The control module then applies this information in determining the deployment rate of the dual-stage airbags. An additional input sensor employed on some Ford Motor Co. vehicles is a driver seat track position sensor. This Hall-effect sensor, located on the driver seat track, informs the control module of the driver's seat position to again help determine the deployment rate of the driver's dual-stage airbag. Of noteworthy mention is the application of a new passive Occupant Classification Sensor (OCS). Although this sensor's engineering design and form is different among auto manufacturers, its purpose fundamentally remains the same. This sensor may be designed with software-programmable weight threshold(s) to help:
Furthermore, these sensors may be used in conjunction with a passenger deactivation switch or become integrated into the control module's software to allow passive deactivation of the passenger airbag. GM's application of an OCS allows for both weight and pattern recognition-based detection. It involves the use of a "Flexpoint Bend Sensor®" mat mounted on top of the passenger seat cushion with an electronic control unit (ECU) attached to it. The ECU communicates input information to the SIR control module. Ford's OCS is made up of a silicone gel-filled bladder mounted in the passenger seat cushion along with both a pressure sensor and ECU mounted to the seat frame. As pressure is applied to the gel-filled bladder from any weight on the front passenger seat, it is transferred through a tube to the OCS sensor. The OCS functions much like a manifold absolute pressure (MAP) sensor on a vehicle's engine by changing the pressure signal into a zero-to-five volt signal. This voltage signal is communicated to the OCS electronic control unit mounted on the seat frame. Based on programmed limits, the OCS electronic control unit informs the SIR control module if the passenger airbag module is to be deactivated or deployed in the event of a collision. Be aware that when servicing passenger seats equipped with an OCS that the SIR system must be deactivated as outlined in the vehicle's service manual. Also, if replacing only the front passenger seat cushion trim cover, the OCS must be re-zeroed. Additional Technologies In addition to dual-stage airbags, most auto manufacturers have begun equipping select models with side airbags that help protect the upper torso of the driver or front seat passenger during a moderate to severe side impact. Only one side airbag will deploy during a side impact and at this point in time, side airbags are not dual-stage. Honda Motor Co.'s side airbag system uses an Occupant Position Detection System (OPDS) that sends occupant height and position data to the SIR control module. This information is used to determine if the passenger is of small stature and if the front passenger is leaning into the side airbag deployment path. If so, the SIR control module will automatically disable the side airbag. The OPDS will also disable the airbag if certain objects are on the seat. As part of the SIR system, be aware that seat belts are equipped with pretensioners to further increase the effectiveness of the seat belt. During a frontal crash, the pretensioners fully retract the belt to remove slack and secure the occupants in their seats. As with inflator modules, these pre-tensioners will require replacement when deployed. As occupant protection technology evolves, so must related service procedures. A serviced occupant safety system is only as good as the technician's repair. For this reason, it is critical that service technicians evolve along with today's changing occupant protection technology.
|
|||||||||||||||||||||||||||||||
Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
| ||||||||||||||||||||||||||||||||
Always assume a deployed dual stage inflator module has an active second stage because it is impossible to visually determine if both stages have been activated. These deployed modules may still contain live pyrotechnic material. Therefore, before disposing of a dual-stage inflator module, it must be reactivated to ensure that both squib igniters have been energized. Improper handling or servicing of an inflator module that contains pyrotechnic material can cause personal injuries or property damage.
Technicians can easily identify a dual-stage inflator module by observing if the module has a total of four wires, instead of the typical two-wire connector. These wires are added through either an additional pair of wires in one connector, or a second two-wire connector (Figure 1). The deployment procedure is similar to a conventional inflator, with the exception that the two squib igniters are connected in parallel and deployed at the same time. General Motors Corp. provides its dealerships with a steering wheel module adapter (J 38826-75) (Figure 2) and an IP module adapter (J 38826-80) to connect the two squibs in parallel. Other manufacturers instruct technicians to simply cut and strip all four wires at the module's connector(s) and twist together one wire from each pair.
Unlike earlier crash sensors that detect sudden deceleration of the vehicle by closing electrical contacts when deployment is warranted, today's crash sensors measure the vehicle's rate of deceleration (i.e., g-force), thus providing an indication of impact severity. For example, Delphi Automotive Systems has developed an Electronic Frontal Sensor (EFS), used on some GM vehicles, that is mounted under the hood near the crush zone. The EFS consists of an accelerometer, a custom integrated circuit (IC) and a microprocessor. Although still only a two-wire sensor, it provides information identifying the severity of the frontal impact to the control module by means of current modulation. This EFS is used in conjunction with other sensor(s) inside the control module. Other auto manufacturers may opt for "single-point" systems with all crash sensor(s) mounted within the control module. Most modern crash sensors consist of some type of accelerometer. If a control module contains internal crash sensors, its orientation in the vehicle is critical. A control module of this type can be identified by an arrow on the case pointing toward the front of the vehicle (Figure 3).
