Design & Function, Electrical, Hydraulic & Mechanical Systems

Roll Bar 

The roll bar (1) consists of a highly rigid steel tube bent in a U-shape, which is inserted into 2 half shells on both sides welded to one another. The 2 main bearings are located at the bottom ends of the roll bar. The mounting points for the support and actuating elements (2 and 8) are located on opposite sides The steel tube is covered with a 30 mm thick layer of PUR foam rubber and matched to the interior fittings. See Fig 1 .

Roll Bar Crash Actuation Trigger Module (N53) 

The roll bar crash-actuated trigger module is located in the rear on the tunnel between the occasional seats. The control module contains 2 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 in 90° angles. See Fig 2 . 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).

• Piezo-Electric Sensor (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.
  Fig 2: Identifying Roll Bar Crash Actuation Trigger Module (N53)

  Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Soft/Hard Top Control Module (N52, As Of 6/95) 

The control module contains 2 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 in 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 2 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 bar. 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 and fault memory (DTC).

• Signal Generation Stage -  The input signals from the 2 rear axle switches (in version used up to approximately 05/95) and the 2 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 greater than 0.4 g¹ ) or a vehicle inclination greater than 22°, the output stage for the belt lock is actuated. In the version used up to approximately 05/95 at a vehicle acceleration rate of greater than 4 g¹ ) or vehicle inclination greater than 22° and when at least one rear axle switch is open, the output stage for the roll bar is actuated.
• Output Stages -  If the control module recognizes a fault, the malfunction indicator lamp is actuated using the corresponding output stage. If the control module recognizes an accident or critical driving situation, the output stage for the roll bar is activated and the roll bar is extended. During a braking maneuver or when driving through a curve the output stage for the seat belts is activated and the belts locked. In the version used up to approximately 05/95 the roll 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 bar okay, roll bar defective, vehicle acceleration greater than 0.4 g¹ ) (g¹ = 9.81 m/s² acceleration due to gravity) and crash actuation.
• Monitor -  The processor itself as well as all electrical components outside are monitored. If any fault is recognized this is indicated to the driver by the malfunction indicator lamp in the instrument cluster coming on. Simultaneously 2 LED's come on in the roll bar switch (convenience feature). This serves as a request to put up the roll bar.
• Fault Memory (DTC) -  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 bar trigger solenoid defective, rear axle switch short circuit to positive or ground (version used up to approximately 05/95) and malfunction indicator lamp. Version used up to approximately 05/95, the stored errors can be recalled using pulse readout on the data link connector.
• Block Diagrams -  Over all functionality of roll bar crash deployment. See Fig 4 .

Soft/Hard Top Control Module (N52, As Of 6/95) 

The roll bar trigger module is integrated into the soft top control module and located in the rear behind the right occasional seat. See Fig 5 . The control module contains 2 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 in 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 2 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 bar. 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 and fault memory (DTC).

• Signal Generation Stage -  The input signals from the 2 rear axle switches (in version up to approximately 05/95) or the signal from the cone-shaped tilt sensor (in version as of approximately 06/95) and the 2 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 greater than 0.4 g¹ ) or a vehicle inclination greater than 22°, the output stage for the belt lock is actuated. In the version up to approximately 05/95 at a vehicle acceleration rate of greater than 4 g¹ ) or vehicle inclination greater than 22° and when at least one rear axle switch is open, the output stage for the roll bar is actuated. As of the version 06/95 the roll bar output stage is triggered at a vehicle acceleration greater than 3 (g¹ ) (g¹ = 9.81 m/s² acceleration due to gravity) or vehicle inclination greater than 52°.
• Output Stages -  If the control module recognizes a fault, the malfunction indicator lamp is actuated using the corresponding output stage. If the control module recognizes an accident or critical driving situation, the output stage for the roll bar is activated and the roll bar is extended. During a braking maneuver or when driving through a curve the output stage for the seat belts is activated and the belts locked. In the version up to approximately 05/95 the roll 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 bar okay, roll bar defective, vehicle acceleration greater than 0.4 g¹ ) (g¹ = 9.81 m/s² acceleration due to gravity) and crash actuation. As of approximately 06/95 the roll 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 any fault is recognized this is indicated to the driver by the malfunction indicator lamp in the instrument cluster coming on. Simultaneously 2 LED's come on in the roll bar switch (convenience feature). This serves as a request to put up the roll bar.
• Fault Memory (DTC) -  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 bar trigger solenoid defective, rear axle switch short circuit to positive or ground (version up to approximately 05/95) and malfunction indicator lamp. Version up to approximately 05/95, the stored errors can be recalled using pulse readout on the data link connector. Version as of approximately 06/95, the fault memory can be read out and erased with the Hand Held Tester (HHT).
• Block Diagrams -  Over all functionality of roll bar crash deployment. See Fig 6 and Fig 7 .

TRIGGERING SOLENOID (Y57/1) 

The triggering solenoid (Y57/1) is located on the right support and actuating element (2). In the event of an accident or critical driving situation it is actuated by the roll bar crash actuated triggering module. This opens the lock (7) which holds the roll bar in the retracted position (A). The roll bar is extended by springs (5). See COMPONENT LOCATIONS  .

ROLL BAR CONVENIENCE SWITCH (S83) 

• The roll bar can also be extended and retracted while driving with the roll bar (convenience) switch (S83) in the center console. This is possible with the soft top up or down or with the hard top attached. The convenience feature is overridden when the soft top or hard top is being moved. In the event of a defect in the roll bar system 2 LED's in the shape of 2 upward pointing triangles flash in the switch (S83). This serves to signal to the driver to put up the roll bar with the convenience feature to ensure protection in the event of an accident or critical driving situation. See COMPONENT LOCATIONS  .
• The roll bar is automatically retracted when the top is being moved to prevent collision between the roll bar and top (roll bar extended), and is extended again after the top motion is completed.
• The convenience feature also serves for retracting the roll bar after crash actuation. For this purpose the switch (S83) must be pressed up in the direction EXTEND for approximately 5 seconds until the lock engages audibly. This causes the hydraulic cylinders to move upward and the lock catches to eventually release. For more information, see Fig 13 and Fig 14 . The roll bar can then be retracted.

MALFUNCTION INDICATOR LAMP (A1E29) 

The malfunction indicator lamp (A1e29) is located in the left half of the instrument cluster. When the ignition key is turned to position 2 in the steering wheel lock the malfunction indicator lamp in the instrument cluster comes on and goes off when the engine starts running as long as a malfunction is not present. If the malfunction indicator lamp continues to burn with the engine running, a malfunction is present. See COMPONENT LOCATIONS  .

REAR AXLE SWITCHES (S83/2 & S83/3) 

The rear axle switches are located on the left and right sides on the spring links for the rear axle. They detect critical driving situations (e.g. rear axle suspension completely extended, rear wheels lifted), which can lead to rolling over. They are designed as normally closed switches. The rear axle switches have 2 positions each and are labeled:

• OPERATION -  In this position the rear axle switch is ready for operation (movable).
• ARRESTED -  In this position the rear axle switch is open and arrested mechanically. This position is necessary for adjustment of the rear axle switch. See COMPONENT LOCATIONS  .

SUPPORT & ACTUATING ELEMENTS 

The roll bar is driven on the right side by a hydraulic cylinder (2). See Fig 8 .

• Mechanical Locking Of Actuating Element
  
  Since the hydraulic circuit is not under pressure when it is not actuated by the convenience feature, the actuating element piston must be locked mechanically in its lower position (A). It is locked by spring force (4) using balls (5). When the convenience feature is actuated, the locking piston (3) and the piston (2) are put under pressure and act against the force of the spring releasing the lock (B). See Fig 9 .
• Crash Actuation -  In the retracted position (A) the support element (2) is held by the lock (7) and the triggering solenoid (Y57/1). The triggering solenoid (Y57/1) is actuated by the control module, opens the lock (7) and the element (2) moves upward (B) within approximately 0.3 seconds under the force of the tensioner spring (5) located in the actuating element. This operation is accompanied by a clicking noise, because the locking pawl (4) engages with the rack during the extension operation beginning at an angle of approximately 14°. This ensures that the roll bar is supported even when it is put under load prematurely. See Fig 10 .
• Convenience Feature (Roll Bar Switch) -  When the convenience feature is actuated the hydraulic element is put under pressure on the piston side (arrow A) when the roll bar is extended, and on the rod side (arrow B) when the roll bar is retracted. This releases the tension on the spring (5) or tensions the spring respectively. The extension speed as well as the extension force of the roll bar (resulting from the spring force and hydraulic force) are controlled by a throttle in the actuating element. To prevent noises when the roll-over is extended (locking pawl rack), the spring-loaded locking pawls (4) are put under pressure on both sides using a hydraulic servo-cylinder and moved away from the rack. See Fig 11 .

  Crash actuation has priority over the convenience feature, i.e. the triggering solenoid can be actuated even when the convenience feature is in operation. In this case the pressure to the servo-cylinder is shut off, the locking pawls (4) swing back to engage in the rack and the roll bar is extended by the force of the spring (5). See Fig 11 . Also, see Fig 13 and Fig 14 , for retracting the roll bar following crash actuation.

3-Point Seatbelt With Electrically Controlled Belt Lock & Emergency Tensioning Retractors  - The complete three-point belt with emergency tensioning retractor is integrated into both front seats. The 3-point belt consists of 3 systems: Vehicle-sensitive locking system, belt-sensitive locking system & emergency tensioning retractor.

NOTE: (g ¹  )  equals 9.81 m/s² (acceleration due to gravity).
• Vehicle-Sensitive Locking System -  In contrast to conventional belt retractors with which the belt is locked by mechanical ball sensors, the control module actuates 2 electro-mechanical relays (K18/2 & K18/3). See COMPONENT LOCATIONS  . These relays lock when they are not actuated. In order to fulfill the legal regulations, which require automatic locking in the event of a power failure, and still allow the belt to be fastened, an additional mechanical release for the locking mechanism is installed which releases the belt locking mechanism using a control cable when the belt is not buckled, i.e. the unbuckled belt is released mechanically and can always be fastened. As soon as the belt is buckled this mechanical release is canceled and the electrical function takes over. The control module is in operation as soon as the ignition is switched ON and the one of the front belts is buckled. After the ignition is switched off or one of the front belts is buckled, a function time delay of 60 minutes exists in both cases for convenience reasons. The front belts are locked (relay not under power), when the control module recognizes one of the following conditions: Vehicle acceleration/deceleration greater than 0.4 g and/or vehicle inclination greater than 22°.
• Belt-Sensitive Locking System -  Which reacts to the belt extension speed, consists of a mechanical mechanism integrated into the retractor.
• Emergency Tensioning Retractors -  The function of the emergency tensioning retractors is the same as previously, whereby the tube points downward. The emergency tensioning retractors are integrated into the front backrests and are activated by the AIRBAG and emergency tensioning retractor control module.
• Child Safety Seat Retention Only -  The electrical belt lock is activated by the seat belt lock switch (S68/13) located on the inside of the passenger seat. After the seat belt has been buckled and the locking tongue inserted into the belt buckle, the seat belt can no longer be pulled out any further, because the switch interrupts the electric belt lock. When the belt buckle is actuated the seat belt is retracted in the usual manner and can be pulled out again. See Fig 12 .

Hydraulic Pump Unit  - The hydraulic unit (pump, motor, supply reservoir) is located in the spare tire recess. If the switch for the roll bar convenience feature or the switch for the soft top is actuated, the pump (A715) runs as long as the switch is pressed, pumping hydraulic fluid at a pressure of approximately 180 bar. The pressure is limited to 180 bar by a pressure limitation valve. See COMPONENT LOCATIONS  .

Valve Block (Y57) Roll Bar -  The roll bar valve block is located in the rear at the right on the center pillar. The solenoid valves are actuated by the soft top control module when the switch for the soft top is pressed. Solenoid valve (Y11) puts up the roll bar, solenoid valve (Y10) retracts the roll bar. The locking pawl is put under pressure moving it away from the rack. See COMPONENT LOCATIONS  .

Roll Bar Crash Actuation Trigger Module-To-Top Actuation Control Module Communication  - The roll bar crash-actuated trigger module is responsible for the crash actuation, the soft top control module for the convenience feature. These modules are connected to one another by 2 wires. The following information is transferred: a) Roll bar okay, b) Roll bar defective, c) Vehicle acceleration/deceleration greater than 0.4 g and d) Crash actuation.

• Roll Bar Okay -  Okay.
• Roll Bar Defective -  When the roll-over bar crash-actuated trigger module recognizes a defect (lamp in instrument cluster comes on), the soft top control module checks whether the roll-over bar is down using the limit switch ROLL BAR DOWN. If the roll- over bar is retracted (limit switch switched) the LED's in the convenience switch are actuated intermittently by the soft top control module. This serves as request to put up the roll-over bar. When the roll bar is extended the LED's go out.
• Vehicle Acceleration/Deceleration Greater Than 0.4 G -  This signal serves as an additional check of the speed signals (electronic speedometer, ABS and ASR). Actuation of the top is over-ridden when the proper speed signals are not present.
• Crash Actuation -  When the soft top control module receives a crash signal from the roll bar crash actuated trigger module, the pressure/electric power to the hydraulic system is switched on immediately if the soft top or roll bar is being moved at the moment.

Function, Crash Actuation & Lowering Following Crash Actuation 

• Roll bar retracted or actuated (crash actuation). Refer to illustration. See Fig 13 .
• Roll bar crash actuated and lowering following crash actuation. Refer to illustration. See Fig 14 .