Restraints and Safety Systems: Description and Operation
System DescriptionSRS Components
Airbags
The SRS is a safety device which, when used with the seat belt, is designed to help protect the driver and front passenger in a frontal impact exceeding a certain set limit. The system consists of the SRS unit, including sating sensor and impact sensor (A), the cable reel (B), the driver's airbag (C), the front passenger's airbag (D), side airbags (E), seat belt tensioners (1), and front impact sensors (J). Since the driver's and front passenger's airbags use the same sensors, both normally inflate at the same time. However, it is possible for only one airbag to inflate. This can occur when the severity of a collision is at the margin, or threshold, that determines whether or not the airbags will deploy. In such cases, the seat belt will provide sufficient protection, and the supplemental protection offered by the airbag would be minimal.
Side Airbags
The side airbags (E) are in each front seat-back. They help protect the upper torso of the driver or front seat passenger during a moderate to severe side impact. Side impact sensors (F) in each door sill and in the SRS unit detect such an impact and instantly inflate the driver's or the passenger's side airbag. Only one side airbag will deploy during a side impact. If the impact is on the passenger's side, the passenger's side airbag will deploy even if there is no passenger.
Seat Belt and Seat Belt Buckle Tensioners
The seat belt and seat belt buckle tensioners are linked with the SRS airbags to further increase the effectiveness of the seat belt. In a front-end collision, the tensioners instantly retract the belt and buckle firmly to secure the occupants in their seats.
OPDS
The side airbag system also includes an occupant position detection system (OPDS). This system consists of sensors (G) and a OPDS unit (H) in the front passenger's seat-back. The OPDS unit sends occupant height and position data to the SRS unit. If the SRS unit determines that the front passenger is of small stature (for example, a child) and the front passenger is leaning into the side airbag deployment path, the SRS unit will automatically disable the passenger's airbag. The SRS unit will also disable the airbag when the OPDS detects certain objects on the seat. When the side airbag is disabled, the side airbag cutoff indicator on the instrument panel alerts the driver that the passenger's side airbag will not deploy in a side impact. When the object is removed, or the passenger sits upright, the side airbag cutoff indicator will go off after a few seconds, alerting the driver that the side airbag will deploy in a side impact.
SRS Operation
The main circuit in the SRS unit senses and judges the force of impact and, if necessary, ignites the inflator charges. If battery voltage is too low or power is disconnected due to the impact, the voltage regulator and the back-up power circuit, respectively, will keep voltage at a constant level.
For the SRS to operate
Driver's and Front Passenger's Airbag(s)
1. A front impact sensor must activate, and send electric signals to the microprocessor.
2. The microprocessor must compute the signals, and depending on the severity of the collision and whether the seat belt is buckled or unbuckled, it sends the appropriate signals to the airbag inflator(s).
3. The inflators that received signals must ignite and deploy the airbags.
Side Airbag(s)
1. A side impact sensor must activate, and send electric signals to the microprocessor.
2. The microprocessor must compute the signals and send them to the side airbag inflator(s). However, the microprocessor cuts off the signals to the front passenger's side airbag if the SRS unit determines that the front passenger's head is in the deployment path of the side airbag.
3. The inflator that received the signal must ignite and deploy the side airbag.
Self-diagnosis System
A self-diagnosis circuit is built into the SRS unit; if the SRS is operating normally, when the ignition switch is turned ON (II), the SRS indicator comes on and goes off after about 6 seconds. If the indicator does not come on, or does not go off after 6 seconds, or if it comes on while driving, it indicates an abnormality in the SRS. The SRS must be inspected and repaired as soon as possible. For better serviceability, the SRS unit memory stores a DTC that relates to the cause of the malfunction, and the unit is connected to the data link connector (DLC). This information can be read with the HDS when it is connected to the DLC(16P).