Roller sun blind, function - GF68.50-P-0004FL

MODEL 212 with CODE 540 (Electric roller blind for rear window) 

Fig 1: Roller Sun Blind Function Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• No overvoltage or undervoltage
• Circuit 15R ON
• Temperature protection is not activated (inside temperature T > 1 °C)

The electronic ignition lock control unit transmits the status of circuit 15 via the interior CAN to the front SAM control unit and the rear SAM control unit.

Roller sun blind, general 

The roller sun blind is located in front of the rear window and can be extended and retracted vertically. When the rear window roller sun blind button in the upper control panel control unit is actuated, the roller sun blind can be extended and retracted manually. During reverse travel the roller sun blind is retracted automatically.

The function includes a soft start-up and delaying of the roller sun blind in a defined range in front of the corresponding mechanical limit stop to reduce wear to the roller sun blind mechanism as well as noise development. This function is called "Soft stop."

The rear window roller sun blind motor is equipped with two Hall sensors. The signals from the Hall sensors are read in and evaluated by the rear SAM control unit.

Thermal protection:

Every time the rear window roller sun blind motor is actuated, it is counted in the rear SAM control unit. If a defined threshold value is exceeded within a fixed time, the rear SAM control unit switches off the rear window roller sun blind motor to prevent overheating. New actuation is only possible after a cooling phase stored in the rear SAM control unit.

The roller sun blind function comprises the following partial functions:

• Function sequence for normalization 
• Function sequence for lockup recognition 
• Function sequence for extending and retracting roller sun blind 
• Function sequence for automatically retracting roller sun blind 

Function sequence for normalization 

It is necessary to normalize the roller sun blind before the first operation. When normalizing the roller sun blind, the upper and lower mechanical end stop of the roller sun blind is actuated and the corresponding position of the rear SAM control unit is stored.

When the rear window roller sun blind is actuated for longer than t = 15 s, the roller sun blind is denormalized. This function can be deactivated via the diagnosis tester. If the voltage of the on-board electrical system is too low, the roller sun blind is also denormalized. Normalizing is the basis for assigning the current position to the position of the roller sun blind sensed by the rear SAM control unit. To normalize manually, press rear window roller sun blind button and hold down until actuation is terminated. The rear window roller sun blind is actuated with reduced speed until the mechanical limit stop is reached and switched off by the blockage detection. The location counter of other limit stop is set to zero Now press rear window roller sun blind button and hold down until the actuation is terminated. The location counter of other limit stop is set to zero Normalization is terminated.

The front SAM control unit reads in the status of the rear window roller sun blind button in the upper control panel control unit via the instrument panel LIN and transmits it to the rear SAM control unit via interior CAN. The rear SAM control unit directly actuates the rear window roller sun blind motor. The roller sun blind is then extended and retracted.

Manual normalization must be accomplished in the following cases:

• Replacement of rear SAM control unit
• Roller sun blind in emergency operation

The roller sun blind is normalized automatically after moving 100 times in normal operation or after lockup.

Function sequence for lockup recognition 

Lockup is recognized, if the Hall sensor signals are missing for a preprogrammed time during extending and retracting.

Failure of the Hall sensor signals can have the following causes:

• Running up against an obstacle within motion area
• Hall sensors defective
• Actuating upper and lower mechanical end stop

The Hall sensor signals from the rear window roller sun blind motor are read in directly by the rear SAM control unit.

In the event of blockage, actuation of the rear window roller sun blind motor is stopped and then reversed. I.e., the roller sun blind is moved in the opposite direction. Then system performs an automatic normalization

Function sequence for extending and retracting roller sun blind 

When the rear window roller sun blind button is pressed, the roller sun blind is requested to extend or retract.

The front SAM control unit reads in the status of the rear window roller sun blind button in the upper control panel control unit via the instrument panel LIN and transmits it to the rear SAM control unit via interior CAN. The rear SAM control unit directly actuates the rear window roller sun blind motor. The roller sun blind is then extended and retracted.

The last direction of motion is stored in the rear SAM control unit, so that the roller sun blind is moved in the direction expected by the operator when the roller sun blind button is actuated again.

If the rear window roller sun blind button is actuated a second time while an actuation is already in progress, the roller sun blind stops and after t = 200 ms it is moved in the opposite direction.

The roller sun blind can be stopped during extending and retracting in each position for test purposes. For this purpose the actuation of the rear window roller sun blind motor can be interrupted manually or via diagnosis tester. Press rear window roller sun blind button three times within t = 500 ms to stop rear SAM control unit. The rear SAM control unit interrupts the actuation of the rear window roller sun blind motor. The roller sun blind remains in the current position.

Actuation time is max. t = 20 s. At an on-board electrical system voltage of U < 10.5 V the actuation time is increased by t = 2 s to ensure that it moves to the end position even under unfavorable conditions (cold, sluggish). After expiration of this time the request is automatically terminated.

If the rear window roller sun blind button is actuated continuously for t > 30 s, it is recognized as "sticking".

Fault handling:

If a defect is recognized, the hardware outputs on the rear SAM control unit are deactivated until the next ignition sequence is started. Various freeze frame data are stored in the rear SAM control unit.