MRS III Control Module
The control module is mounted in the center console area on the driveshaft tunnel below the center storage box. The X5 will use the TEMIC system that can be recognized by the green 50 pin connector on the module.
The control module contains the processing electronics (Smart Technology) for triggering of all air bags and pyrotechnic devices installed in the vehicle. Two electronic deceleration sensors are installed in the module for crash or impact detection.
Scheme 2
Satellite Sensors
The satellite sensors are mounted below the driver's and passenger's front seats on the seat frame. The function of the sensors is to detect the severity of side impacts and signal the MRS III control module, through a pulse modulated signal, in the event of a crash. The control module uses this input signal along with its internal impact sensor signal to determine the deployment of the side/head airbags.
As with the control modules, the satellite sensors are manufacturer specific. The Temic sensors in the X5 have a three wire connector which will not interchange with the Bosch sensors. Only two of the wires are used for the satellite sensor's operation. The signal for deployment of the bags is carried over the power wire of the sensor.
Scheme 3
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Driver's Front Airbag
With the MRS III system, the driver's front airbag becomes a two stage bag similar to the passenger's front side bag, introduced on the 1999 model E38/E39s. The complete assembly is mounted beneath the cover in the center of the steering wheel as with previous airbags. The assembly now contains the inert gas generator chamber and two ignition stages (ignitors).
The airbag consists of
Scheme 5
- Accumulator/gas generator
- Two ignition capsules
- Propellant gas - 13.5% hydrogen/86.5% oxygen
- 64 liter airbag
Passenger's Front Airbag
The passenger's front airbag is the same unit as installed on E38/E39 vehicles as of 9/98 production. The passenger's airbag consists of
Scheme 6
Scheme 7
- Pressure accumulator/gas generator
- Two ignition capsules - for two stage activation
- Propellant gas of - 13.5% hydrogen/86.5% oxygen
- 105 liter airbag
Side Airbags Front/Rear (Thorax)
The side airbags continue to be mounted in the door panels on the front and rear doors. Deployment of the side airbags is dependent on the triggering thresholds programmed in the MRS III control module, based on the inputs from the satellite sensors and internal crash sensor.
The side airbags use the same cold gas inflation method as the driver's and passenger's front bags.
Scheme 8
Head Airbag (ITS)
The head airbags are similar to the ITS bags used on the MRS II system. They continue to be mounted from the "A" pillar up along the headliner and are anchored behind the "B" pillar. The ITS bags of the MRS III system are also the cold gas inflation type. The head airbags are always triggered with the side (Thorax) bags.
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Battery Safety Terminal (BST)
As with previous systems, the BST is used to disconnect the battery's "B+" connection to the engine compartment in the event of an airbag deployment. The safety measure helps prevents the possibility of a short circuit causing a fire.
Scheme 11
Seat Belt Tensioners
The seat belt tensioners are a new design and also make use of the inert gas for triggering. The MRS III control module will deploy the seat belt tensioners based on the programmed parameters during impact.
Scheme 12
Seat Occupancy Sensor (SBE)
The SBE continues to be used as an input to the MRS III control module for detection of a front seat passenger. The module uses the input to determine seat belt tensioner and/or front airbag deployment.
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Triggering Thresholds - Two Stage Airbags
The programming of the MRS III includes four triggering thresholds for the two stage front airbags. The triggering of the front airbags is also dependent on whether the seat belts are connected and if the front passenger seat is occupied. The triggering thresholds for the two stage airbags are as follows
| THRESHOLD | NO-SEATBELT | BELTED |
|---|---|---|
| 1 | Ignition Stage 1 | No Activation |
| 2 | Ignition Stage 1 & 2 with Time Delay | Ignition Stage 1 |
| 3 | Ignition Stage 1 & 2 with Time Delay | Ignition Stage 1 & 2 with Time Delay |
| 4 | Ignition Stage 1 & 2 Simultaneously | Ignition Stage 1 & 2 Simultaneously |
TRIGGERING THRESHOLDS - TWO STAGE AIRBAGS
If the signal from the SBE is defective on triggering, the MRS III will deploy as if the seat is occupied.
If the signal from the seat belt contacts are defective, the MRS III will deploy as if the belts were not buckled.
Scheme 14
Side Airbags/ITS
The triggering thresholds for the side airbags/ITS is dependent on the signals from the satellite sensors and the crash sensor in the MRS III control module. The triggering thresholds are independent of the belt tensioners.
Belt Tensioner
The triggering of the belt tensioners is dependent on the signal from the seat belt contact and the severity of the impact as detected by the control module.
Battery Safety Terminal
The BST will deploy in a frontal impact at threshold 2 or greater. The threshold for BST activation with a side impact is programmed separately in the side deployment criteria. The BST will also be deployed when the rear impact threshold is exceeded.
Fuel Pump Shut-Down
New to the MRS III system is the link via the K-Bus/CAN Bus to the Engine Control Module for deactivation of the fuel pump. The MRS III will signal the DME over the K-Bus through the instrument cluster and CAN Bus to shut off the fuel pump in the event that any crash threshold is exceeded.