Air Bag Systems: Description and Operation
AIRBAG CONTROL MODULE (ACM)Airbag Control Module (ACM) Location:
The Airbag Control Module (ACM) contains the impact sensor and energy reserve capacitor. The impact sensor acts as a threshold sensitive switch that completes a circuit when an impact provides sufficient deceleration. The sensor is calibrated for the specific vehicle and reacts to the severity and direction of the impact.
The ACM monitors the system to determine the system readiness. The ACM stores sufficient energy to deploy the airbags for approximately two minutes after the battery is disconnected. The ACM contains on-board diagnostics, and illuminates the AIRBAG warning lamp in the cluster when a diagnostic trouble code occurs. The warning equipment is tested for a few seconds every time the vehicle is started.
CLOCKSPRING
Clockspring:
The clockspring is mounted to the steering column behind the steering wheel. The clockspring consists of a flat, ribbon like, electrically conductive tape that winds and unwinds with the steering wheel rotation.
The clockspring is used to maintain a continuous electrical circuit between the wiring harness and the:
- Driver's airbag module
- Speed control switches Horn switch
Driver Airbag Module:
DRIVER AIRBAG MODULE
WARNING: NEVER DISASSEMBLE THE DRIVER OR PASSENGER AIRBAG MODULES, THERE ARE NO SERVICEABLE PARTS WITHIN THE MODULES.
The Driver Airbag Module located in the center of the steering wheel is the most visible part of the system. It contains the airbag cushion and its supporting components. The airbag module contains a housing in which the cushion and inflator are attached and sealed.
The driver side inflator assembly is mounted from the back of the module housing. When supplied with the proper electrical signal, the inflator assembly produces a gas and discharges it directly into the cushion. A protective cover is fitted to the front of the Driver Airbag Module and forms a decorative cover in the center of the steering wheel. The Driver Airbag Module is mounted directly to the steering wheel.
Driver Airbag Module:
PASSENGER AIRBAG MODULE
WARNING: NEVER DISASSEMBLE THE DRIVER OR PASSENGER AIRBAG MODULES, THERE ARE NO SERVICEABLE PARTS WITHIN THE MODULES.
The Passenger Airbag Module is located beneath the decorative cover of the instrument panel, facing the passenger seat.
The PAB module is mounted to the instrument panel and pad assembly. The passenger inflator assembly is within the module housing. The module is mounted to the instrument panel retainer and support structure. A protective cover is fitted into the instrument panel over the airbag module and forms a decorative cover.
The Passenger Airbag Module (PAB) consists of:
- Inflator assembly
- Reaction canister
- Airbag Pillow
- Deployment door
When supplied with the proper electrical signal the inflator will produce a gas and discharge it directly into the cushion.
When supplied with the proper electrical signal, the inflator produces gas and discharges it directly into the pillow. The deployment door will hinge, allowing the pillow to fully inflate.
Seatbelt Control Timer Module (SCTM) Location:
SEATBELT CONTROL TIMER MODULE (SCTM)
This vehicle uses a convertible structural seatbelt system. Anchors hold the belt to the seat rather than the body. Embodied in the belt system is a Retractor-Integrated Height Adjuster. The purpose of the height Adjuster is to accommodate a wide range of occupant sizes.
The SCTM is mounted near the center of the vehicle. A G-sensor is located inside the module.
This belt system attaches to a reclinable seat back so the traditional locking pendulum mechanism would not provide security. A solenoid was designed to lock the belt and was made part of each of the retractor mechanisms to each seat back. An impact sensor deactivates the solenoids. The impact sensor is a component of the Seatbelt Control mer Module (SCTM) located under the center console.
The G-sensor is sensitive to frontal impact and to a roll or pitch or more than 45 degrees and to acceleration or deceleration equal to or greater than 0.7G in any direction.
STRUCTURAL SEAT BELT SYSTEM
The structural seat with integrated Retractor Integrated Height Adjuster allows the seat belts to comfortably fit a large range of occupants. The seat belts are attached to the seat instead of the body, this allows better passenger access to the rear seat.
Since the retractor is mounted on a seat back that can recline, a typical seat belt g-sensor cannot be used in the retractor. Instead, a solenoid inside the retractor is used to lock and unlock the seat belt when electrically signaled by a remote g-sensor. The remote g-sensor is located inside the Seat belt Control mer Module (SCTM). The SCTM is located under the center console. The seat belt retractor solenoid is located in the seat back and is serviced as a assembly.
When the solenoids are powered, the seat belt can be moved. When the solenoids are not powered, the seat belts can not be extracted. This is necessary to ensure that occupants are always safe, even in the case of a power loss during an accident. Whether the seat belts are in lock or unlock position, an occupant can always release the seat belt and it will retract.
The Seat Belt Control mer Module controls the power to the seat belt solenoids. It supplies power continuously to the seat belts whenever the ignition key is in the RUN or ACCESSORY position. The module has two other unique functions: that of a timer and a g-sensor.
The Seat Belt Control Timer Module was designed with a timer function so that when the vehicle is not in use, the battery would not be prematurely drained. The module times out after approximately 30 minutes if no inputs are send to the module. The module will power the seat belts for a set period of time when there is a input:
- Either door ajar switch (open or closed)
- Ignition switch moved from RUN or ACCESSARY to the OFF position.
Each time one of these input occurs, the timer is reset to keep the belts powered for 30 minutes.
The G-Sensor function of the Seat Belt Control Timer Module will cut power to the seat belt whenever:
- The vehicle accelerates or decelerates at a rate greater than or equal to 0.7g in any direction.
- The vehicle is tilted to an angle greater than or equal to 45 degrees.
Input of ignition switch in the RUN or ACCESSORY position will cause the module to power the seat belts as long as the condition exists.
The SCTM incorporates limited diagnostics. The detectable faults include solenoid shorted to ground, open or shorted to battery, internal fault, or no acceleration within the past 10 timer cycles. Faults are communicated to the seatbelt lamp via a single fault line to another module. The other module communicates the fault on the bus to the cluster/lamp.