The multiple restraint systems MRS3 and MRS4 consist of a control module, two sensors for detecting a side impact, a sensor for detecting seat occupancy of the passenger's seat (not R5x), and inflator assemblies for triggering the airbags.
The multiple restraint system MRS4 is a development of the MRS3 system.
All inflator assemblies and sensors are connected to the MRS control module. The control module registers and evaluates the sensor data. In the event of a frontal or side-on collision, the internal control-module logic decides whether airbag triggering is required and which airbags have to be triggered.
For crash detection, the MRS control module contains acceleration sensors that use the deceleration values to assess the accident situation. In the event of a side-on crash, the external side sensors (satellites) are also evaluated.
In addition to all inputs and outputs, the MRS control module also monitors internal components. Possible fault statuses are stored in nonvolatile form in the control module and indicated to the driver by means of the Airbag Warning Lamp (AWL).
Based on the current maximum configuration, the MRS multiple restraint system consists of the following 11 ignition power circuits:
The airbag warning lamp indicates to the driver the proper functioning of the overall MRS system.
The MRS control module starts a self-test after the ignition has been switched on. The airbag warning lamp is lit during this test period (approx. 3 - 5 s) and then goes out if no faults are found.
The failure warning lamp will light up permanently if the MRS control module detects a current fault or a fault code that has already been stored during the test or during driving.
A seat belt buckle check facility is fitted in USA version vehicles.
The MRS control module receives information as to whether the seat belt is buckled from a switch in the belt buckle.
Based on this belt buckle monitoring function, the control module decides whether the seat belt tensioners need to be triggered in the event of a crash and whether the airbag needs to be triggered at stage 1 (seat belt not buckled) or stage 2 (seat belt buckled).
The satellites are sensors mounted in the side area of the vehicle on the cross members beneath the driver's and passenger's seats. They are connected by a data line to the MRS control module.
In this way, in the event of a side impact collision all airbags on the side of the vehicle facing the point of impact can be triggered.
However, the side and head airbags are only triggered if both the sensor and the MRS control module have detected acceleration.
The MRS control module is connected to the K-bus on all model series equipped with a K-bus. For model series without K bus (Z3 and Z3 Coupé), there is a completion with a connection on the diagnosis bus (TxD line).
Diagnosis and encoding are conducted via the bus.
The task of the MRS is to define the type of collision with the aid of sensors. Within fractions of a second, the information is then evaluated, passed on to the corresponding inflator assemblies and the airbag triggered.
The intensity of an impact is determined based on the detected acceleration values and one or several ignition power circuits are triggered depending on the determined value.
NOTE: Unintentional airbag operation must not occur even in extreme driving situations.
The front airbags (driver and passenger airbag) support the function of the seat belts and prevent the head from making contact with the steering wheel or dashboard in the event of a head-on collision.
2-stage airbags are used for the driver and passenger.
Only stage 1 of the front airbag or stage 1 and stage 2 are triggered depending on the detected intensity of the impact. A variable delay time that is also calculated on the basis of the acceleration values is set between ignition of both airbag stages.
On the country-specific version for the USA, an additional differentiation is made as to whether the occupants have their seat belts buckled. If the occupants do not have their seat belts buckled, the triggering thresholds are lowered so that the airbags are triggered earlier in stage 1 and stage 1/2.
The side and head airbags protect the occupants in the event of a side impact collision. The main task of the side airbags is to support the body in the side chest area. Front ITS (ITS = Inflatable Tubular Structure) prevents injuries in the head and neck area.
All side airbags and ITS airbags are controlled separately on the left-hand and right-hand sides of the vehicle.
In the event of a side impact collision, all side airbags and ITS airbags are triggered simultaneously on the side facing the source of impact.
The task of the seat belt tensioners is to take up slack in the seat belt and hold the body securely in the seat in the event of a collision. In fractions of a second, the belt buckle is pulled back by gas pressure; this simultaneously tightens the shoulder and lap belt, effectively preventing the body from slipping under the lap belt.
The seat belt tensioners are triggered both in the event of frontal impact as well as a rear-end collision if the triggering threshold for the belt tensioners is exceeded.
To reduce the risk of fire in the event of a frontal impact, the ignition power circuit for battery isolation is also activated when the airbag is triggered.
In this case, a gas generator (safety battery terminal) isolates the heavy-current lead (terminal 30) from the battery to the starting motor/alternator.
CAUTION!
All work on the airbag must only be conducted with the battery disconnected!
Connect and disconnect control module, sensors and inflator assemblies (gas generators) only with the battery disconnected!
The MRS control module contains vehicle-specific data and must therefore be encoded before placing into operation!
Removal and installation in other vehicles is prohibited!