Design, Control Module
Design, Control Module
The task of the supplemental restraint system module (SRS) is to reduce driver and passenger injuries in the event of different types of accidents. This is carried out by the control module validating incoming collision pulse signals, that is the acceleration signals, triggered by a collision, and to select an action.
The control module has an internal sensor as assistance, as well as the external crash sensor. The system selects one of the following to activate based on the collected data:
- front airbags.
- the side impact protection (SIPS) bags.
- the inflatable curtains.
- the seat belt tensioner.
The crash sensor in the supplemental restraint system module (SRS) registers the longitudinal mechanical stresses which occur in the event of a frontal collision. A side impact can also be registered by the crash sensor. The longitudinal stresses are measured using two acceleration sensors. When the longitudinal stresses exceed a certain level a calculation of the stress (the collision pulse) starts.
This evaluates if the impact was great enough to activate the airbags and/or the seat belt tensioners. The seat belt tensioners can be activated without the air bags being activated, or vice versa.
Airbags and seat belt tensioners can be activated individually. Driver and passenger airbags and seat belt tensioners are designed to deploy in the event of a frontal collision.
When the collision protection system is activated, the control module transmits a current pulse to the ignition mechanisms in the airbags and/or the seat belt tensioners. No seat belt tensioners or airbags will be activated in the event of a collision from the rear.
Two requirements need to be fulfilled in order for the side impact protection system to be activated. One; that the collision pulse is so high that a trigger signal is sent from the side impact sensor to the control module. Two; the control module or another collision sensor transmits a confirmation signal which makes it possible for the collision protection system to deploy. When the control module has received a trigger signal and a confirmation signal, the side impact protection system can deploy.
If the side impact occurred at the front of the vehicle the side airbags and the inflatable curtain are deployed on the side that received the impact. If the side impact occurred at the rear of the vehicle only the inflatable curtain is deployed.
The control module has a collision recording function. This records certain system information in the event of a collision. The information can be analyzed and used after a collision if required.
This information is used to develop the collision safety systems of the future.
In the event of a collision the supplemental restraint system module (SRS) transmits a collision signal to the phone module (PHM) and the central electronic module (CEM) via a directly connected cable.
The purpose of the signal is to switch off the fuel pump, to light the interior lighting, to unlock the doors, and if the car is equipped with Volvo On Call (Plus), to transmit an automatic alarm to the Customer Service Center when the vehicle is involved in an accident. This also applies in the event of a collision from the rear.
A collision signal is also sent to the phone module (PHM) and the rear electronic module (REM) via the controller area network (CAN).
The control module decides to deploy either the airbags or the seat belt tensioner. This is based on:
- Whether the driver and passenger front seat belts are being used or not.
- If there are faults in the side impact sensor or the terminals for.
- the side impact sensor.
- If there are faults in the seat belt buckle.
- If the Controller area network (CAN) communication does not function.
Depending on the situations mentioned above, this may mean that in the event of a low speed collision the seat belt tensioner on the driver's side activates while the airbag deploys on the passenger side.
Information about the use of the seat belt buckle depends on the model year. The differences are:
- For model year 1999-2002: Information about the use of the driver and passenger seat belt buckles comes from the central electronic module (CEM) (4/56) on the controller area network (CAN). A diagnostic trouble code (DTC) is stored in the central electronic module (CEM) if the fault occurs in the driver's or passenger front seat belt buckle. The central electronic module (CEM) sends this information on to the supplemental restraint system module (SRS) which stores a corresponding diagnostic trouble code (DTC).
- For model year 2003: The driver and passenger seat belt buckles are directly connected to the supplemental restraint system module (SRS).
The SRS (supplemental restraint system) indicator lamp lights with the ignition on. If no faults are found by the control module, either internally or on the sensor, wiring or igniter, a signal is transmitted via the Controller Area Network to the driver information network to switch off the SRS warning lamp. If a fault occurs, the supplemental restraint system module (SRS) transmits information to the driver information module (DIM) about which lamp to light and the text to be displayed in the combined instrument panel. The driver information module (DIM) continuously transmits information to the supplemental restraint system module (SRS) via the controller area network (CAN) about the status of the SRS indicator lamp. If the SRS (supplemental restraint system) indicator lamp stops functioning the red light in the general warning lamp is used instead.
NOTE: After a collision the wiring to the airbags and/or seat belt tensioners which have deployed must be replaced. The reason is that the connectors can melt at the moment of deployment. If a connector has melted, the closest wiring must be replaced.
WARNING: The ignition must be switched off before carrying out work on the SRS (supplemental restraint system). Otherwise the airbags can deploy by mistake.