Introduction
ROLLOVER PROTECTION SYSTEM (RPS):
The E36 Convertible has an available Rollover Protection System (RPS) to supplement the protection afforded by the integral reinforcement in the windshield frame. The system consists of two cassettes each containing a retracted roil bar mounted behind the rear seat headrests.
When the system is activated, the spring loaded roll bars rise up until they reach the limit of their travel, or until the bars are physically restrained by the soft top or hard top assembly. The bars are prevented by retracting by a racheting rack and pawl system.
Each cassette is independent, but they are both actuated by a single control module which is bolted to the left cassette.
The control module that controls both units consists of: (see illustration)
The system is designed to deploy the roll bars whenever the control module senses a situation that might cause the car to roll over. This can happen when:
- The vehicle approaches its lateral angle limit (approximately 62°).
- The vehicle experiences a lateral acceleration of approximately 3 G's.
- A combination of lateral acceleration and lateral angle approach a point sufficient to cause the vehicle to roll over.
- The vehicle approaches its longitudinal angle limit (approximately 72°).
- The vehicle experiences a longitudinal acceleration of approximately 3 G's.
- A combination of longitudinal acceleration and longitudinal angle approach a point sufficient to cause the vehicle to roll over (forward direction only).
- The vehicle becomes airborne and achieves weightlessness for at least 80 ms.
The control module senses the above (except for weightlessness) by means of the inclinometer built into the control unit. The inclinometer is comprised of three liquid filled tubes with air bubbles. If the vehicle is tilted or accelerated enough, the air bubbles in one of the tubes travels through the tube, passing by an LED. A photo transistor mounted across from the LED senses a change in density of the liquid when the bubble crosses the beam, and sends a signal to the processing chip. The control unit then sends a signal to the actuator solenoids on each cassette, releasing the restraining catches, and the roll bars extend.
As with SRS, the backup power supply capacitors allow the system to function even if vehicle power is interrupted in an accident.
Weightlessness is determined by a spring loaded sensor mounted within the control module.
When the vehicle becomes airborne, the spring (3) pushes up the magnet (2) when the gravitational force exerted on the magnet is reduced to the point where it can be overcome by the spring. The magnet travels upward to the point where the reed contact (1) closes and sends a signal to the processing chip. If this signal is received for more than 80 ms, the system is deployed.
Once the system has been deployed, it must be reset before the soft top can be operated. To reset, remove the screwdriver handle from the tool kit, and attach to the special tool. Remove the head restraints and the plastic caps on the roll bars. Insert the tool in front of the left hand section of each roll bar to release the pawl from the rachet rack. It may be necessary to pull up slightly on the roll bar to get the pawl to release. Depress the roll bar about 20 mm, remove the special tool, and depress the roll bar completely until the solenoid actuator has engaged the catch.
The system can be activated by using the BMW Service Tester or the MoDiC. It must be tested at each Inspection I or II, and no less than once every two years.
WARNING: If a cassette must be removed, it should be deployed first, to eliminate the chance of accidental activation while handling.
If a cassette cannot be activated using the tester or MoDiC, there is an access hole provided in the front of the cassette to allow for manual activation.