Control Module
The primary task of the supplemental restraint system is to reduce the degree of injury to the driver and passengers in various types of accidents. To do so, the Supplemental Restraint System Module (SRS) analyzes the retardation that arises during a collision and chooses appropriate action.
The control module is aided in its task by internal and external sensors. Based on sensor data, the control module determines whether any of the following should be deployed:
- front airbags
- side impact protection (SIPS) bags
- inflatable curtains
- seat belt tensioners
- adaptive steering column (USA/CDN only)
- adaptive seatbelt force limiter (only XC60 or USA/CDN).
Retardation that exceeds a certain value triggers a calculation that evaluates whether the collision is of sufficient force to deploy any of the protection systems.
The driver and passenger airbags and the seat belt tensioners as well as inflatable curtains are designed to deploy in the event of a frontal collision as necessary. For XC60 or in USA/CDN, the adaptive steering column and the function for adaptive seatbelt force limiting are also activated as necessary.
In case of a side collision, front belt tensioners (presuming the passengers are wearing seat belts) plus the side airbag and inflatable curtain closest to the area of impact are deployed as necessary.
In the event of a rear-end collision, only the front belt tensioners are deployed (presuming the passengers are wearing seat belts).
Supplemental Restraint System Module (SRS) can also register if the vehicle is about to roll over (only XC60). As help for this, the module features a roll-over sensor.
If the vehicle's rotational energy exceeds a certain level, the control module starts a calculation if the roll-over protection is to be deployed. All seatbelt tensioners and inflatable curtains are deployed if roll-over protection is activated.
The Supplemental Restraint System Module (SRS) also has a collision registration function that saves system information in case of a collision. The purpose of this is to enable analysis of collision data for refinement Volvo's collision safety system.
Vehicles on USA/CDN-markets set a non-erasable trouble code in case of a collision that has resulted in activation of a protection system. In these cases the Supplemental Restraint System Module (SRS) must be replaced.
On other markets an erasable code is set in case of a collision. The trouble code can only be erased after collision data has been read out and the memory location has been unlocked. Unlocking means that the memory location once again can be used for storing collision data. When the control module has been involved in four collisions that have resulted in activation of some safety system, a non-erasable trouble code is set. In these cases the Supplemental Restraint System Module (SRS) must be replaced.
In the event of a forceful enough frontal collision, sideways collision or back-end collision, or roll-over (only XC60), a collision signal is transmitted from the Supplemental Restraint System Module (SRS) to the Phone Module (PHM) and the Central Electronic Module (CEM) using a directly connected cable. The purpose of this signal is to:
- switch off the fuel pump (FP)
- switch off the windshield wipers when the car is stationary
- turn off defrosting of windows and rearview mirrors if the vehicle is stationary
- light the interior lighting
- light the flashing hazard lights
- unlock the central locking system
- send an automatic alarm to CSC (Customer Service Center) when an accident has occurred - provided the vehicle is equipped with Volvo On Call (Plus).
- turn off the fuel engine heater
A collision signal is also sent to the Phone Module (PHM) and the Central Electronic Module (CEM) via the Controller area network (CAN).
The Supplemental Restraint System Module (SRS) decides to deploy the airbags and/or the belt tensioners in the event of a frontal collision.
This decision is based on factors such as:
- whether the driver and front passenger are wearing seat belts
- whether the front passenger airbag has been disabled
- the status of the belt buckles
- the status of CAN communication.
Based on the status of the above factors, a low-speed collision could, for example, trigger deployment of the belt tensioner on the driver's side and the airbag on the front passenger side.
Supplemental Restraint System Module (SRS) communicates with Closing Velocity Module (CVM) (only XC60), the main function of which is to prevent or minimize damage in case of frontal collisions.
Vehicles with Closing Velocity Module (CVM) have no front impact sensor. For more information, see: DESIGN
Closing Velocity Module (CVM) continuously sends information to Supplemental Restraint System module (SRS).
Supplemental Restraint System Module (SRS) uses the information as an early indication if the vehicle is about to collide, and can in this way prepare any actions. Also Closing Velocity Module (CVM) continuously sends information to Supplemental Restraint System Module (SRS) about its status and reliability.
The SRS indicator lamp lights when the ignition is switched on. If no faults are registered by the control module, neither internally nor from the sensors, wiring or igniters, a signal is transmitted via the CAN to the Driver information module (DIM) confirming that the SRS indicator lamp can be switched off. If there is a fault, the Supplemental Restraint System Module (SRS) transmits information to the Driver Information Module (DIM) indicating which lamp should be lit and the text to be displayed in the combined instrument panel:
- The SRS warning lamp
- the general warning lamp or
- the yellow information lamp.
The Driver Information Module (DIM) continuously transmits information to the Supplemental Restraint System Module (SRS) control module via the controller area network (CAN) about the status of the SRS warning lamp.
If for some reason the SRS warning lamp is not operational, the general red warning lamp is used instead.
Note that after a collision, it may be necessary to replace the wiring harness for the components of the protection system which have deployed. This is because the connectors may melt at the moment of deployment. If a connector has melted, the wiring harness adjacent to the connector must be replaced.