Restraints and Safety Systems: Description and Operation
General Information:
The driver airbag unit in the steering wheel, in conjunction with the belt tensioners for the seat belts and the energy-absorbing panels on the driver's side, serve to increase the level of protection provided by the three-point seat belts installed as standard equipment, when these are worn.
Both systems are electrically activated by a single control unit in the event of moderately severe to severe frontal collisions. Current knowledge indicates that the entire (intact) driver airbag unit maintains its full functional reliability for at least 10 years. In contrast to the three-point seat belt which only affords protection when it is applied, the occupant of the vehicle has no influence over the protective effect of the airbag and belt tensioner restraint system. For increased protection it is essential that the three-point seat belt is applied and the restraint system consisting of driver's airbag and belt tensioner is installed. The restraint system of driver's airbag and belt tensioner, only provides increased protection in the event of a frontal collision. An occupant not wearing the three-point seat belt remains unprotected in side and rear end collisions, or if the vehicle overturns.
1 Airbag unit
2 Belt tensioner
3 Control unit (sensor)
4 Reserve power source
5 Voltage transformer
6 Energy-absorbing panel under dashboard (drivers side) (USA)
7 Warning lamp
Driver Airbag (USA) as of 9/87:
1 Driver airbag unit
3 Belt tensioner (left and right)
4 Control unit
5 Energy absorbing panel under dashboard, driver's side (USA)
7 SRS warning lamp
Driving with the Airbag and Belt Tensioner Restraint System:
A1e15 - RS Warning Lamp:
When the ignition key is moved from ignition key position "1", the red warning lamp marked "RS" or "SRS" in the instrument cluster lights up.
The warning lamp indicates the readiness of the airbag and belt tensioner restraint system. It must light up from key position "1", and go out again after approx. 10 s in vehicles up to 09/87, or after approx. 4 s in vehicles as of 09/87. If it does not light up, or fails to go out after the specified period, or if it lights up when driving, there is a fault in the system. The time of the fault is registered by the control unit and can be called up at a later date.
WARNING: If this fault display appears, the entire system must be examined as soon as possible by specialist personnel using the airbag tester (in vehicles up to 09/87) or by means of pulse output (in vehicles as of 09/87).
This does not impair the operation of the driver's and passenger's seat belts installed as standard equipment.
The full airbag and belt tensioner restraint system consists of the following components: ("A" was intentionally omitted from the following list.) (Refer to respective component for more details.)
B. Driver airbag unit
C. Belt tensioner unit
D. Control unit
E. Reserve power source (up to 09/87)
F. Warning lamp
G. Voltage transformer (up to 09/87)
H. Energy-absorbing panel under the dashboard (USA only)
Design:
Driver Airbag Unit:
The driver airbag unit consists of:
- signal carrier
- cushion with integral airbag
- retaining plate
- gas generator
The safety element proper is the airbag which is inflated within 25 ms to fill the space between the driver and the steering wheel.
9 Steering wheel
51 Driver airbag unit
52 Gas generator
55 Plug connection
The complete driver airbag unit is bolted to the steering wheel installed in the vehicle after connecting the special plug connection (55).
51 Driver airbag unit
52 Gas generator
53 Gas generator plug connection
55 Plug connection
56 Generator carrier with special nuts.
Before the driver airbag unit is fitted in the vehicle, it is electrically shorted automatically by means of a short-circuiting link. The short-circuiting link is automatically opened when the plug connection (55) is plugged in.
Method of Operation:
When the control unit sends the appropriate electrical pulse (ignition pulse) to the detonator located inside the gas generator, the solid fuel in the gas generator is ignited. The fuel burns within an extremely short time releasing a certain quantity of gas at a certain pressure. The gas is guided into the airbag via filters.
The nylon fabric airbag folded on top of the gas generator tears open the cushion at a predetermined breaking point. The gas rigidly inflates the airbag, thus preventing the driver's head from colliding with the steering wheel. After approx. 60 ms the gas has escaped through 4 vents or through a filter section in the airbag, and the airbag collapses.