Lexus IS250 IS220d GSE20 ALE20 - SUPPLEMENTAL RESTRAINT SYSTEM
AIRBAG SYSTEM - SYSTEM DESCRIPTION
| GENERAL |
In conjunction with 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 knee of the driver and front passenger. This system is a 3-sensor type airbag system to detect the impact during a front collision using the center airbag sensor assembly and front airbag sensors. It also operates the airbag system and seat belt pretensioner.
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.
In conjunction with 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.
The curtain shield airbag that helps reduce shock to the front and rear seat occupants with a single curtain shield airbag has been adopted. In conjunction with this system, the side airbag sensors have been installed at the bottom of the center pillars and the rear airbag sensors have been installed at the bottom of the rear pillars.
In this system, a front side collision is detected by the side airbag sensor in order to simultaneously deploy the side airbags and the curtain shield airbags. A rear side collision is detected by the rear airbag sensor and the center airbag sensor assembly in order to deploy the curtain shield airbags.
The center airbag sensor assembly sends the airbag deployment signal to the ECM through CAN (Controller Area Network) to operate the fuel pump control.
The center airbag sensor assembly sends the airbag deployment signal to the main body ECU via the discrete line to operate collision door lock release control.
| CONSTRUCTION AND OPERATION |
FRONT AIRBAG SENSOR
The front airbag sensors are installed on the right and left radiator supports respectively.
The front airbag sensor consists of the deceleration sensor.
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.
SIDE AIRBAG SENSOR
The side airbag sensors are installed on the bottom of the right and left center pillars respectively.
The side airbag sensor consists of the deceleration sensor and ignition control circuit.
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.
REAR AIRBAG SENSOR
The rear airbag sensors are installed on the right and left rear pillars respectively.
The rear airbag sensor consists of the deceleration sensor and ignition control circuit.
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.
CENTER AIRBAG SENSOR ASSEMBLY
General
Deceleration sensor and ignition control circuit
Safing sensor
Electronic safing sensor
Backup power source
Diagnostic circuit
Memory circuit
SRS WARNING LIGHT
The SRS warning light is located on the combination meter assembly. It comes on to inform the driver of system trouble when a malfunction is detected in self-diagnosis of the center airbag sensor assembly. Under normal operating conditions when the engine switch is turned on (IG), it comes on for approximately 6 seconds and then goes off.
AIRBAG CUT OFF SWITCH CYLINDER
The manual cut off switch (airbag cut off switch cylinder) is mounted on the side instrument panel RH. By turning the manual cut off switch to the OFF position with ignition key, the front passenger airbag can be disabled.
| DEPLOYMENT CONDITION |
When the vehicle collides and the shock is greater than the specified value, the SRS is activated automatically. The center airbag sensor assembly includes the safing sensor and deceleration sensor. The safing sensor is designed to turn on at a smaller deceleration rate than the deceleration sensor.
The center airbag sensor assembly determines whether or not 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 front collision, the ignition signal could be output with the deceleration sensor ON signal even without a signal from the front airbag sensor.
The center airbag sensor assembly determines whether or not 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.
The center airbag sensor assembly determines whether or not 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 assembly deploys, the curtain shield airbag assembly will also deploy, regardless of whether the signal is output from the rear airbag sensor.