Part 1
Design
Control module
Warning! The battery must be disconnected before any work is carried out on the supplemental restraint system (SRS). Otherwise the airbags could accidentally deploy.
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/CAN only)
- adaptive seatbelt force limiter.
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, belt tensioners and inflatable curtain deploy as necessary in the event of a head-on collision. The adaptive steering column and the adaptive seatbelt force limitation function are also triggered 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 case of a rear-end collision, only the front seatbelt pretensioners are deployed (presuming the passengers are wearing seatbelts).
Supplemental Restraint System Module (SRS)can also register if the vehicle is about to roll over. 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. The control module can store information about two collisions.
Vehicles on USA/CAN-markets set a non-erasable trouble code in case of a collision that has resulted in deployment of an airbag (does not apply to deployed knee airbag). 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, 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), the main function of which is to prevent or minimize damage in case of frontal collisions.
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 warning lamp lights when the ignition is switched on. If no faults are registered by the control module - either internally or from the sensors, wiring or igniters - a signal is transmitted via the CAN network to the driver information module (DIM) confirming that the SRS warning 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 text should displayed in the combined instrument panel and which of the following lamps should be lit:
- The SRS warning lamp
- the general warning lamp
- the yellow information lamp.
The driver information module (DIM) continuously transmits information to the supplemental restraint system (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.
Warning! The battery must be disconnected before any work is carried out on the supplemental restraint system (SRS). Otherwise the airbags could accidentally deploy.
Side impact sensor
The vehicle's side impact sensors are used to provide the supplemental restraint system (SRS) early information on a side-on collision.
The four sensors used in the car are:
- 1 side impact sensor in each left and right B post (A)
- 1 side impact sensor in each left and right C post (B)
- 1 side impact sensor (pressure sensor) in each left and right front door (C).
The side impact sensors in the B and C posts consist of acceleration sensors that continuously send data to the control module.
The side impact sensors (pressure sensors) in the doors consist of air pressure sensors that continuously transmit data to the control module.
In case of a collision Supplemental Restraint System Module (SRS) uses data from the sensors and from an acceleration sensor, installed internally in the control module, to decide if the collision force is sufficient to active the side impact protection.
The control module generates one or more diagnostic trouble codes if one or both of the side impact sensor fail. A diagnostic trouble code is also generated if communication between the control module and either of the side impact sensors fails.
If one (or both) of the side impact sensors stops working for some reason, the control module uses information from the other sensors to determine when to deploy the impact protection.
Data is transmitted on the same cable used for power supply. There is a signal/power supply cable to each side impact sensor and a ground cable.
The four side impact sensors in the B and C posts are of the same type, therefore, they can be installed in all four positions.
The side impact sensors (pressure sensors) in the doors are of the same type and can be installed in either the left or right-hand doors.
Each front impact sensor has a specific ID that is used to check that the right front impact sensor is installed in the vehicle.
Roll-over sensor
The roll-over system consists of a roll-over sensor of the type pyro sensor, which senses the vehicle's angle (lean).
The roll-over sensor is used to give the Supplemental restraint system module (SRS) early information in case of a roll-over.
If the vehicle's sideways angle changes fast enough, then Supplemental Restraint System Module (SRS) will start a calculation how high the rotation energy is. If the rotation energy is high enough, the control module will activate the roll-over protection.
The roll-over protection activates all seatbelt tensioners and inflatable curtains in the vehicle.
In case of incorrect signal from the roll-over sensor, the control module generates a diagnostic trouble code.
The roll-over sensor is installed on the circuit board on Supplemental Restraint System Module (SRS).
Switch front passenger airbag (not USA/CAN)
With the switch it is possible to deactivate the airbag for the front passenger. The switch is located on the side of the instrument panel, on the passenger side.
The switch is only accessible when the front side door on the passenger side is open. The key blade in the remote control is used to change the position of the switch.
With the switch in position "OFF", all steps for the airbag are deactivated and the warning light airbag passenger (PAD) is lit.
When the switch is in position "ON", the passenger airbag is activated and warning light activated airbag passenger (PAE) is lit.
The switch position is determined using two Hall sensors. The Hall sensors for the switch are directly connected to Supplemental restraint system module (SRS).
Each Hall sensor is separately connected to the control module. The signal that is sent from the Hall sensors consists of two different current levels depending on which position the switch is in.
If the signal from the Hall sensor cannot be interpreted correctly, a diagnostic trouble code is generated and the control module may, depending on the problem, choose to deactivate the passenger airbag.
If the passenger airbag is deactivated then warning light airbag passenger (PAD) as well as the SRS-warning light are lit and a text message is shown in the Driver information module (DIM).
If problems are detected and the passenger airbag cannot be deactivated, then warning light activated airbag passenger (PAE) as well as the SRS-warning light are lit instead and a text message is shown in the Driver information module (DIM).
Note! The front passenger airbag switch and occupant weight sensor (OWS) must not both be installed in the vehicle.
Occupant weight sensor (OWS) (USA/CAN only)
The occupant weight sensor (OWS) consists of three interactive components:
- Pressure sensor and silicon pad, installed under the seat cushion in passenger seat front.
- Belt tension sensor, mounted in the seat frame on the outside of the front passenger seat.
- Occupant weight sensor module, installed under the front passenger seat.
The pressure sensor and silicon pad are linked with a hose. The pressure sensor registers the pressure to which the seat cushion, that is, the silicon pad, is exposed. For example, when someone is sitting in the seat.
Information from the belt tension sensor is also used to ensure the good performance of the system. The belt tension sensor informs the occupant weight sensor module what force the belt is tensioned with. This is done because the pressure measured by the pressure sensor can be affected by the passenger fastening the seatbelt tightly. This means that the passenger exerts greater pressure on the seat than during normal seatbelt use. The passenger is then interpreted as being heavier than he or she is.
Using information from both the pressure sensor and belt tension sensor, the occupant weight sensor performs calculations that give Supplemental Restraint System Module (SRS) the following information:
- Passenger seat empty - airbag passenger front off.
- Passenger seat child - airbag passenger front off.
- Passenger seat big - airbag passenger front on.
The occupant weight sensor (OWS) transmits continuous signals on the internal controller area network (CAN), which the supplemental restraint system module (SRS) and occupant weight sensor (OWS) are connected to. If the occupant weight sensor (OWS) does not function correctly the supplemental restraint system module (SRS) will:
- disable the front passenger airbag
- light the passenger airbag warning lamp (PAD) in the roof console
- light the SRS (supplemental restraint system) warning lamp and display the alert message in the driver information module (DIM).
If a fault occurs in any of the components the following should be noted:
- The pressure sensor and occupant weight sensor module must be replaced at the same time
- The belt tension sensor is replaced separately.
Note! The switch for activating, on/off, the front passenger airbag and occupant weight sensor (OWS) must not be installed in the vehicle together.
Front airbags
Warning! Never use an ohmmeter or similar tool to test airbags, inflatable curtains, adaptive belt force limiters, adaptive steering column or belt tensioners. Disconnect airbags, inflatable curtains, adaptive seat belt limiters, adaptive steering column or belt tensioners before testing them. Failure to do so may result in accidental deployment, which in turn could result in serious injury or death.
The airbags at the front of the vehicle are:
- driver airbag, 2 stage deployment
- front passenger airbag, 2 or 3-stage deployment.
The driver's airbag is located in the steering wheel. The passenger airbag is located above the glove compartment in the dashboard.
Each airbag stage has a separate igniter component. These are electrically separated from each other. This means that the different ignition components have their own separate power supply and grounding points from the control module.
During airbag deployment, electrical signals are transmitted from the supplemental restraint system module (SRS) to the relevant airbag stage.
Stage 1
Stage 1 of the driver's airbag is pyrotechnic. In the event of deployment, the charge combusts and the gas which develops is blown into the airbag.
Stage 1 on the passenger airbag consists of a pyrotechnic component in combination with a reservoir which stores a gas. In the event of deployment, the pyrotechnic charge combusts and mixes with the stored gas. The gas mixture inflates the airbag.
Stage 2
Stage 2 of the driver's and passenger airbags is pyrotechnical. In the event of deployment, the charge combusts and the gas which develops is blown into the airbag.
The time lapse of the airbag's 2-stage deployment depends on the type of collision and seat belt usage. Both stages are always deployed. In the event of a minor collision, there is a long delay between stages 1 and 2, generating a soft airbag. In the event of a severe collision, there is a short delay between stages 1 and 2, generating a harder airbag.
Stage 3 (front passenger airbag only - USA/CAN)
Stage 3 of the front passenger airbag is pyrotechnical. Upon deployment, a valve opens on the airbag.
Using information from the seat position sensor, belt buckle sensor and impact sensor, the control module can adjust the stiffness of the airbag to the severity of the collision. This is done by ventilating the airbag.