Air Bag Systems: Description and Operation
SUPPLEMENTAL RESTRAINT SYSTEM: AIRBAG SYSTEM: SYSTEM DIAGRAM
SYSTEM DESCRIPTION
1. GENERAL
(a) In conjunction with the impact absorbing structure for a front collision, the SRS (Supplemental Restraint System) driver airbag, front passenger airbag, driver side knee airbag, and front passenger side knee airbag were designed to supplement seat belts in the event of a front collision in order to help reduce shock to the head, chest, and knees of the driver and front passenger. This system is a 3-sensor type airbag system which detects the impact during a front collision using the center airbag sensor and front airbag sensors. It also operates the airbag system and seat belt pretensioner.
(b) In order to detect the extent of the collision during the initial stages of the collision in further details, the front airbag sensors have been changed from mechanical type to electrical type deceleration sensors. Accordingly, the deployment of the driver airbag and front passenger airbag is controlled in two stages according to the severity of the impact.
(c) In conjunction with the impact absorbing structure for a side collision, the side airbag and curtain shield airbag were designed to help reduce shock to the driver, front passenger, and rear outer passengers in the event of a side collision.
(d) The curtain shield airbag helps reduce shock to the front and rear seat occupants. In conjunction with the curtain shield airbag, side airbag sensors are installed at the bottom of the center pillars and rear airbag sensors are installed at the bottom of the rear pillars.
(e) In this system, a front side collision is detected by the side airbag sensor in order to simultaneously deploy the front seat side, rear seat side, seat cushion airbag, and curtain shield airbags. A rear side collision is detected by the rear airbag sensor and the center airbag sensor in order to deploy the rear seat side airbags, seat cushion airbag and curtain shield airbag.
(f) The center airbag sensor sends the airbag deployment signal to the ECM through CAN (Controller Area Network) to operate the fuel pump control.
(g) The center airbag sensor sends the airbag deployment signal to the main body ECU via the discrete line to operate collision door lock release control.
2. CONSTRUCTION AND OPERATION
(a) FRONT AIRBAG SENSOR
(1) The front airbag sensors are installed on the right and left radiator supports respectively.
(2) The front airbag sensor consists of a deceleration sensor.
(3) The deceleration sensor is built into the front airbag sensor, and the distortion that is created in the sensor is converted into an electric signal based on the vehicle deceleration rate during a frontal collision. Accordingly, the extent of the initial collision can be detected in detail.
(b) SIDE AIRBAG SENSOR
(1) The side airbag sensors are installed on the bottom of the right and left center pillars respectively.
(2) The side airbag sensor consists of a deceleration sensor and an ignition control circuit.
(3) The deceleration sensor is built into the side airbag sensor, and the distortion that is created in the sensor is converted into an electric signal based on the vehicle deceleration rate during a front side collision. Accordingly, the extent of the initial collision can be detected in detail.
(c) REAR AIRBAG SENSOR
(1) The rear airbag sensors are installed on the right and left rear pillars respectively.
(2) The rear airbag sensor consists of a deceleration sensor and an ignition control circuit.
(3) The deceleration sensor is built into the rear airbag sensor, and the distortion that is created in the sensor is converted into an electric signal based on the vehicle deceleration rate during a rear side collision. Accordingly, the extent of the initial collision can be detected in detail.
(d) CENTER AIRBAG SENSOR
(1) General
* The center airbag sensor is installed on the center floor under the instrument panel.
* The center airbag sensor consists of a deceleration sensor, safing sensor, electronic safing sensor, ignition control circuit, and diagnostic circuit.
* The center airbag sensor receives signals from the deceleration sensor and safing sensor built into the center airbag sensor and front airbag sensor. Then the center airbag sensor determines whether the driver airbag, front passenger airbag, driver side knee airbag, front passenger side knee airbag, front seat belt pretensioners and rear seat belt pretensioners should be activated, and diagnoses system malfunctions.
* The center airbag sensor causes the front side, rear side, and curtain shield airbags to deploy when receiving signals from the side airbag sensors.
* The center airbag sensor receives signals from the deceleration sensor and the electronic safing sensor built into the center airbag sensor and the rear airbag sensor, and determines whether the rear seat side, seat cushion and curtain shield airbag should be activated, and diagnoses system malfunctions.
* The center airbag sensor sends the airbag deployment signal to the ECM through CAN to operate the fuel pump control.
* The center airbag sensor sends the airbag deployment signal to the main body ECU through the discrete line to operate collision door lock release control.
(2) Deceleration sensor and ignition control circuit
* The deceleration sensor is built into the center airbag sensor.
* The ignition control circuit performs calculations based on the signal output from the deceleration sensors of the center airbag sensor and front airbag sensor. If the calculated values are greater than the specified values, it activates an ignition operation.
(3) Safing sensor
* The safing sensor is built into the center airbag sensor. During a front collision, the sensor turns on and outputs an ON signal to the center airbag sensor if a deceleration rate sent to the safing sensor is greater than the specified value.
(4) Electronic safing sensor
* The electronic safing sensor is built into the center airbag sensor. During a side collision, the sensor turns on and outputs an ON signal to the center airbag sensor if a deceleration rate sent to the electronic safing sensor is greater than the specified value.
(5) Backup power source
* The backup power source consists of a power supply capacitor and a DC-DC converter. When the power system does not function during a collision, the power supply capacitor discharges and supplies electric power to the system. The DC-DC converter operates as a boosting transformer when the battery voltage falls below a predetermined level.
(6) Diagnostic circuit
* This circuit constantly diagnoses system malfunctions. When a malfunction is detected, it turns on the SRS warning light on the combination meter to inform the driver.
(7) Memory circuit
* When a malfunction is detected in the diagnostic circuit, it is coded and stored in the memory circuit.
(e) SRS WARNING LIGHT
(1) The SRS warning light is located on the combination meter. It comes on to inform the driver of system trouble when a malfunction is detected in the self-diagnosis of the center airbag sensor. Under normal operating conditions when the engine switch is turned on (IG), it comes on for approximately 6 seconds and then goes off.
3. DEPLOYMENT CONDITION
If the vehicle collides and the shock is greater than the specified value, the SRS is activated automatically. The center airbag sensor includes the safing sensor and deceleration sensor. The safing sensor is designed to turn on at a lower deceleration rate than the deceleration sensor.
(a) The center airbag sensor determines whether ignition is necessary based on signals from the deceleration sensor and the front airbag sensor (*1). If the safing sensor turns on simultaneously, current flows to the squibs to deploy the SRS as shown in the illustration below.
HINT
*1: In case of a front collision, the ignition signal could be output with the deceleration sensor ON signal even without a signal from the front airbag sensor.
(b) The center airbag sensor determines whether ignition is necessary based on signals from the side airbag sensor. If the safing sensor turns on simultaneously, current flows to the squib to deploy the SRS as shown in the illustration below.
(c) The center airbag sensor determines whether ignition is necessary based on signals from the rear airbag sensor. If the safing sensor turns on simultaneously, current flows to the squib to deploy the SRS as shown in the illustration below (*1).
HINT
*1: If the front seat side airbag deploys, the rear seat side airbag, seat cushion airbag, and the curtain shield airbag will also deploy, regardless of whether the signal is output from the rear airbag sensor.
(d) The center airbag sensor determines whether ignition is necessary based on signals from the deceleration sensor. If the safing sensor turns on simultaneously, current flows to the squibs to deploy the SRS as shown in the illustration below.
