The multiple restraint system MRS 4 Re-Design consists of a control unit for detecting a side-on crash, a sensor for detecting seat occupancy of the passenger seat, and inflator assemblies for triggering the airbags. The external sensors are divided into: two front airbag sensors, two door satellites and two B-pillar satellites.
The multiple restraint system MRS 4 Re-Design is a development of the MRS 4 system.
All inflator assemblies and sensors are connected to the MRS control unit. The control unit registers and evaluates the sensor data. In the event of a frontal or side-on collision, the internal control-unit logic decides whether airbag triggering is required and which airbags have to be triggered.
For crash detection, the MRS control unit contains two acceleration sensors arranged at an angle of 90 degrees. These use the braking values that occur to assess the accident situation. In the event of a head-on collision, the external front airbag sensors and B-pillar satellites are also evaluated. In the event of a side-on crash, the external door satellites and B-pillar satellites are also evaluated.
In addition to all inputs and outputs, the MRS control unit also monitors internal components. Possible fault statuses are stored in non-volatile form in the control unit 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 15 triggering circuits:
The airbag warning lamp indicates to the driver the proper functioning of the overall MRS system.
The MRS control unit 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 unit detects a current fault or a fault code that has already been stored during the test or during driving.
Die airbag warning lamp shows the driver the airbag status on the passenger's side.
On the US country version, an extended seat occupation detection (OC3) is fitted. This reports the current occupation status of the passenger's seat to the MRS control unit. Under certain conditions, the MRS control unit switches off the airbags for the front passenger's seat although it is occupied. In this case, the airbag warning lamp lights up.
A seat belt buckle check facility is fitted in USA version vehicles.
The MRS control unit 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 unit decides whether the 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 front airbag sensors consist of an acceleration sensor to register a head-on collision. The front airbag sensors are connected by a data line to the MRS control unit.
Whether the driver's or front passenger's airbag as well as the seatbelt tensioners are triggered is determined by the acceleration values of the sensors, the B-pillar satellites and the MRS control unit.
The door satellites are sensors consisting of an acceleration sensor or a pressure sensor to register a side-on crash. The door satellites are connected by a data line to the MRS control unit.
Whether the side and head airbags are triggered is determined by the acceleration or pressure values of the sensors, the B-pillar satellites and the MRS control unit.
The B-pillar satellites are sensors consisting of two acceleration sensors. They are positioned at an angle of 90 degrees to each other. The B-pillar satellites are connected by a data line to the MRS control unit.
Whether the side and head airbags are triggered is determined by the acceleration values of the door satellites and the MRS control unit.
Whether the driver's or front passenger's airbag as well as the seatbelt tensioners are triggered is determined by the acceleration values of the front airbag sensors and the MRS control unit.
A seat mat that changes its resistance as weight load increases is located under the seat cushion of the passenger seat. This change in resistance is evaluated by the electronic seat occupancy control system and determines the status ”seat occupied” or ”seat not occupied”. The result is then passed on to the MRS control unit.
Corresponding to this information, in the event of a head-on collision, the control unit can activate the triggering circuits for passenger airbag and passenger belt tensioner if the passenger seat is occupied.
The extended seat occupation detection OC3 consists of a seat mat on which pressure-sensitive sensors are fitted. In addition, the seat mat has a hard-wire connection to an electronic evaluation unit. The weight classification is based on evaluating the impression created by the person when taking their seat. The seat occupation detection cannot measure weights. Due to the activation of individual cells of the sensor mat, a weight class is determined by the electronic evaluation unit. The electronic evaluation unit sends cyclical information on the classification to the MRS control unit.
Corresponding to this information, in the event of a head-on collision, the control unit can activate or deactivate the triggering circuits for passenger airbag and passenger belt tensioner.
The MRS control unit is connected to the K-bus on all model series equipped with a K-bus.
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 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.
The passenger airbag and belt tensioner on the passenger side are not triggered if the control unit recognises that the passenger seat is not occupied.
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) and rear head airbags prevent injuries in the head and neck area.
All side airbags, ITS and rear head 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, ITS and head airbag are triggered simultaneously on the side facing the source of impact.
For triggering the airbag on the passenger side in the event of a side impact, the following information applies:
The task of the 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 tensions the shoulder and lap belt, thus effectively preventing the body from slipping under the lap belt.
The 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 firing 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 starter motor/alternator.
CAUTION!
All work on the airbag must only be conducted with the battery disconnected!
Connect and disconnect control unit, sensors and inflator assemblies (gas generators) only with the battery disconnected!
The MRS control unit contains vehicle-specific data and must therefore be encoded before placing into operation!
Removal and installation in other vehicles is prohibited!