Description of Function of Airbag with Seat Belt Tensioner D. - Automatic Seat Belt Wearing Comfort Facility - ra9100140d600x(0600)

Model 140 

General 

The risk of injury to the head and chest in the case of serious frontal collisions is further reduced by means of the driver's/front passenger's airbag unit in combination with the three-point seat belt and the energy-absorbing covers on the driver's and/or front passenger's side.

The driver's and front passenger's airbag units are marked "SRS Airbag". The warning light is marked SRS (Supplemental Restraint System).

Both systems are activated electrically by means of a control device in the event of a moderate to serious frontal collision. Our present knowledge indicates that, if undamaged, the entire airbag and seat belt tensioner restraint system should have a fully operational life of at least ten years. In contrast to the three-point seat belt, which only offers protection when worn, the vehicle occupant cannot influence the protection afforded by the airbag and seat belt tensioner system in any way. A properly worn three-point seat belt and the driver's airbag and front passenger's seat belt tensioner system are essential if this increased protection is to be fully effective.

The airbag and seat belt tensioner restraint system offers increased protection in the event of a frontal collision only. No protection at all is offered to a vehicle occupant not wearing a three-point seat belt in the event of a side collision, rear collision or roll-over.

Fig 1: Identifying Airbag Function For Seat Belt Tensioner

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's Airbag 

Fig 2: Identifying Driver's Airbag Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's/Front Passenger's Airbag 

Fig 3: Identifying Driver's/Front Passenger's Airbag Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's Airbag USA Version 

Fig 4: Identifying Driver's Airbag (USA Version) Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driver's/Front Passenger's Airbag USA Version 

Fig 5: Identifying Driver's/Front Passenger's Airbag (USA Version) Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Arrangement of Components 

Driver's Airbag with Seat Belt Tensioners 

Fig 6: Components Arrangement - Driver's Airbag With Seat Belt Tensioners

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Arrangement of Components 

Driver's/Front Passenger's Airbag with Seat Belt Tensioners 

Fig 7: Components Arrangement - Driver'S/Front Passenger's Airbag With Seat Belt Tensioners

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

NOTE: In the case of vehicles in the version the components listed are located in the same position.

Stick-on Label for Replacement Date of the Driver's Airbag Unit 

The stick-on label with the replacement date of the airbag unit is located on the left-hand center pillar below the belt fastener.

Fig 8: Identifying Label For Replacement Date Of Driver's Airbag Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Stick-on Label for Replacement Date of the Driver's/Front Passenger's Airbag Unit 

On the left-hand center pillar below the belt fastener there is a stick-on label with the replacement date of the driver's and front passenger's airbag unit. The replacement date refers to the entire driver's and front passenger's airbag unit in each case. The operating life is at least ten years.

Fig 9: Identifying Label For Replacement Date Of Driver's/Front Passenger'S Airbag Unit

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Driving with the Airbag and Belt Tensioner Restraint System 

When the ignition key is in position "1", the red warning light with the "SRS" symbol in the instrument cluster should light up.

The warning light shows that the airbag and seat belt restraint system is in proper working order. In ignition key position "1" it should light up for approx. 4 secs and then go out again. If it fails to light up or to go out after the stated time, there is a fault in the system. The error time is recorded by the control device (N2/2) and can be read out afterwards.

Fig 10: Locating SRS Warning Light

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Should an error be indicated in the above-mentioned- way, the entire system must be checked as exhaustively as possible by trained staff via impulse output.

The operation of the standard-fitted driver's and front passenger's seat belts is not impaired by such a fault.

The complete airbag and seat tensioner restraint system consists of the following components:

1. Driver's airbag unit
2. Front passenger's airbag unit
3. Seat belt tensioner unit
4. Control device
5. Warning light
6. Energy-absorbing cover under dashboard (driver's and front passenger's side)

D. Automatic Seat Belt Wearing Comfort Facility 

Fig 11: Identifying Automatic Seat Belt Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

For reasons of comfort, automatic seat belt reels for the front seats and, in the case of electrical individual seat adjustment of the back seats, also the back seats are equipped with a so-called seat belt wearing comfort facility.

The aim of the seat belt wearing comfort facility is to achieve the greatest possible reduction of the pulling and stretching forces created on the seat belt wearer by the automatic seat belt rewind system.

Principle Diagram 

Fig 12: Identifying Automatic Seat Belt Function

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Design 

Main components

• Rewind spring (strong)
• Comfort spring (weak)
• Revolving housing with outer toothing
• Operating magnet in automatic inertia reel
• Switch (contact) in the seat belt locks

Arrangement and Operation of the Springs (1, 2) 

• Rewind spring (1), strong Attachment inside on the revolving housing and outside on the device cover.
• Comfort spring (2), weak

Attachment inside (radial) on the rewinder shaft and outside on the revolving spring housing.

Seat belt not attached (seat belt lock open) → normal rewind function (strong spring)

Seat belt attached (seat belt lock closed) →

Comfort function (weak spring)

Function 

By means of the corresponding power transfer the weak spring is pulled onto the block in its normal state and is thus inoperative. The system now only performs rewinding functions.

When the tongue of the lock is inserted into the seat belt lock, the operating magnet (K18/4, K18/5) is activated via terminal 15C, and this blocks the revolving movement of the housing in the rewinding direction by activating a locking lever which engages in the outer toothing of the revolving housing, thereby decoupling the strong spring. The weak spring, until this point pulled against the block, now has a reduced effect on the rewinder shaft. The comfort range is preset.

Assuming a comfortable position to be that when the belt is pulled tight around the body when put on and locked, comfort is increased by further reducing the belt forces in accordance with the subsequent intentional or unintentional stretching of the belt.

Fig 13: Arrangement And Operation Of Springs

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.