Roll Bar Control Module: Description and Operation

Roll-over bar crash-actuated trigger module (N53) up to approx. 05/95

The roll-over bar crash-actuated trigger module is located in the rear on the tunnel between the occasional seats. The control module contains two piezo-electric sensors 1), which measure the vehicle acceleration in the longitudinal direction (X) and lateral direction (Y).
They are located in the control module correspondingly (90 ° angles).
The signal from the sensor elements are proportional to the acceleration and are processed mathematically according to the laws of trigonometry, whereby a constant acceleration sensitivity is achieved in any desired direction in the horizontal plane. A position switch senses the vehicle inclination (all around).






Soft top control module (N52) as of approx. 06/95

The roll-over bar trigger module is integrated into the soft top control module and located in the rear behind the right occasional seat.
The control module contains two piezo-electric sensors 1), which measure the vehicle acceleration in the longitudinal direction (X) and lateral direction (Y).
They are located in the control module correspondingly (90 °angles).
The signal from the sensor elements are proportional to the acceleration and are processed mathematically according to the laws of trigonometry, whereby a constant acceleration sensitivity is achieved in any desired direction in the horizontal plane.
The control module contains two cone-shaped tilt sensors. The first actuates at a vehicle inclination of 22 ° all the way around. The belt lock is controlled by this sensor. A second cone- shaped tilt sensor replaces the previous rear axle switch and senses critical situations which can lead to roll-over. This cone-shaped tilt sensor trips at a vehicle inclination of 52 ° triggering the roll-over bar.

1) A damped, piezo-ceramic bender bar mounted in the sensor is bent due to its inertia by negative acceleration, e.g. crash, braking, etc., producing a voltage. This voltage serves for measurement of the acceleration.

All signals are generated and processed digitally.

The electronic control module is subdivided functionally into:
- Acceleration sensors (X and Y)
- Signal generation stage
- Processor
- Output stages
- Monitor
- Error memory

Signal generation stage
The input signals from the two rear axle switches (in version up to approx. 05/95) or the signal from the cone-shaped tilt sensor (in version as of approx. 06/95) and the two front belt buckles (buckled, not buckled) are converted by the signal generation stage to a form which can be used by the processor.

Processor
In the processor the signals for vehicle acceleration and vehicle inclination are evaluated and compared with set values. If the processor recognizes a vehicle acceleration rate > 0.4 g 1) or a vehicle inclination > 22 °, the output stage for the belt lock is actuated. In the version up to approx. 05/95 at a vehicle acceleration rate of > 4 g 1) or vehicle inclination > 22 ° and when at least one rear axle switch is open, the output stage for the roll-over bar is actuated. As of the version 06/95 the roll-over bar output stage is triggered at a vehicle acceleration > 3 g 1) or vehicle inclination > 52 °

Output stages
If the control module recognizes an error, the malfunction indicator lamp is actuated via the corresponding output stage.
If the control module recognizes an accident or critical driving situation, the output stage for the roll-over bar is activated and the roll-over bar extended. During a braking maneuver or when driving through a curve the output stage for the seat belts is activated and the belts locked.

1) 1 g approx. equal to 9.81 m/sec.sq. (acceleration due to gravity)

In the version up to approx. 05/95 the roll-over bar crash-actuated trigger module and the soft top control module are connected by a data bus (2 lines), which transfers the following information:
- Roll-over bar okay
- Roll-over bar defective
- Vehicle acceleration > 0.4 g 1)
- Crash actuation

As of approx. 06/95 the roll-over bar control module is integrated into the soft top control module.

Monitor
The processor itself as well as all electrical components outside are monitored. If an error is recognized this is indicated to the driver by the malfunction indicator lamp in the instrument cluster coming on. Simultaneously two LED's come on in the roll-over bar switch (convenience feature). This serves as a request to put up the roll-over bar.

1) g approx. equal to 9.81 m/sec.sq. (acceleration due to gravity).

Error memory
The following errors are recognized and stored in a non-volatile memory (EEPROM).
- Control module defective
- Voltage too low
- Left belt locking relay defective
- Right belt locking relay defective
- Roll-over bar trigger solenoid defective
- Rear axle switch short circuited to plus or ground (version up to approx. 05/95)
- Malfunction indicator lamp

Version up to approx. 05/95
The stored errors can be called via pulse readout on the data link connector.

Version as of approx. 06/95
The error memory can be read out and erased with the HHT.






Block diagram, overall function, roll-over bar on version up to approx. 05/95






Block diagram, overall function, roll-over bar on version as of approx. 06/95