Liftgate control, function - GF80.20-P-0003GR

MODEL 166 up to model year 2016 with CODE 890 (EASY-PACK liftgate)

Fig 1: Liftgate Control Block Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general

Circuit 30g ON
No overvoltage or undervoltage
Liftgate control normalized
Speed v < 1 km/h (relevant as of circuit 15R ON)
Vehicle inclination < 20 %
Play/overload protection not active

The electronic ignition lock control unit sends the status of circuit 15 to the liftgate control unit via the interior CAN.

The instrument cluster sends the vehicle speed to the liftgate control unit via interior CAN.

A play protection counter is integrated into the liftgate control unit to protect against thermal overload of the electric liftgate control motor. It senses the number of actuations or the number of opening and closing procedures. A total of 20 actuators or 10 complete opening and closing operates are permitted. The play protection counter is decremented by one for each second it is not active. In addition, a thermo switch is integrated into the electric liftgate control motor to monitor the heat development in the electric liftgate control motor. If overload of the electric liftgate control motor is recognized via the thermo switch, the liftgate control unit interrupts the power supply. The liftgate remains in the momentary position. The opening/closing procedure can be continued only after the liftgate control electric motor has cooled down to normal level.

Liftgate control, general

The liftgate can be opened or closed automatically from inside and outside via the liftgate control.

It is always possible to open or close the liftgate manually, however, with slightly increased force.

The liftgate control function comprises the following partial functions:

Function sequence for opening and closing request
Function sequence for opening liftgate
Function sequence for closing liftgate
Function sequence for synchronizing liftgate
Function sequence for opening angle limitation
Function sequence for obstacle detection

Function sequence for opening and closing request

The liftgate can opened and closed from the following control points:

Open/close liftgate button on transmitter key
Driver trunk lid/liftgate control button
Tailgate control button
Tailgate external operation switch

If the liftgate control unit reads in another request while the liftgate is opening or closing, the liftgate drive stops. Only when requested again, the drive is continued. except: Operation with transmitter key. When the liftgate close/open button on the transmitter key is actuated again after stopping, the liftgate moves in the opposite direction. If the liftgate is positioned at the limitation point when the liftgate open/close button on the transmitter key is actuated, the liftgate is also moved in the opposite direction.

Open/close liftgate button on transmitter key

Vehicles except CODE 889 (KEYLESS-GO):

When the liftgate open/close button on the transmitter key is pressed for t > 0.5 s, it transmits a radio signal to the electronic ignition lock control unit via the rear window antenna and FM 1, AM, CL and KEYLESS-GO antenna amplifier.

Vehicles with CODE 889 (KEYLESS-GO)

When the liftgate open/close button on the transmitter key is pressed for t > 0.5 s, it transmits a radio signal to the KEYLESS-GO control unit via the rear window antenna and FM 1, AM, CL and KEYLESS-GO antenna amplifier.

The KEYLESS GO control unit transmits the access authorization code to the electronic ignition lock control unit via interior CAN.

The electronic ignition switch control unit checks the access authorization of the transmitter key.

If it is defined as valid, the electronic ignition lock control unit transmits the request "Open liftgate" or "Close liftgate" to the liftgate control unit via the interior CAN.

The transmitter key must be located in the direct vicinity of the vehicle. The operation radius of the transmitter key (range of radio signal) corresponds to the central locking function.

Driver trunk lid/liftgate control button

The left front door control unit directly reads in the status of the driver trunk lid/liftgate control button and transmits this to the liftgate control unit via the interior CAN.

Tailgate control button

The rear SAM control units directly reads in the status of the liftgate control button and transmits it to the liftgate control unit via the interior CAN.

MODEL 166 up to model year 2016 with CODE 889 (Keyless Go) with CODE 890 (EASY-PACK liftgate)

In addition the central locking can be locked via the liftgate control button. Detailed information concerning this can be found in the separate partial function "KEYLESS-GO".

Tailgate external operation switch

The rear SAM control units directly reads in the status of the liftgate external operation switch and transmits it to the liftgate control unit via the interior CAN.

Additional function requirements for opening liftgate

Opening request is present

Function sequence for opening liftgate

The liftgate control unit reads in the corresponding opening request from the interior CAN, evaluates them and transmits the request "Open liftgate" to the rear control unit via the interior CAN. The rear control unit then actuates the liftgate control locking motor. It actuates the locking pawl in the liftgate lock and releases the rotary tumbler. The position of the locking pawl (locked/unlocked) is defined via the status of the liftgate locking pawl switch and read in by the rear control unit. The position of the locking pawl (locked/unlocked) is defined via the status of the liftgate rotary tumbler switch and read in by the rear control unit. The rear control units directly reads in the status of the liftgate locking pawl switch and the liftgate rotary tumbler switch to the liftgate control unit via the interior CAN.

Then the liftgate control unit actuates the electric liftgate control electric motor in the opening direction until the liftgate control position sensor recognizes the upper limitation point or the opening angle limitation.

The speed with which the liftgate is opened, is reduced momentarily before reaching the upper limit stop (braked). For this purpose the liftgate control unit evaluates the signals from the liftgate control Hall sensor and the liftgate control position sensor.

If the liftgate is opened as a result of the request via the driver trunk lid/liftgate control button or the open/close liftgate button on the transmitter key, the liftgate control unit actuates the liftgate control warning buzzer 2 times during the liftgate movement. A warning tone does not sound when the request comes from the liftgate external operation switch.

When the liftgate control unit does not receive signals from the liftgate control position sensor, the actuation is of the liftgate control electric motor is stopped. Moving the liftgate is possible by hand with slight force.

If the liftgate control drive unit is defective, it must be replaced completely.

Additional function requirements for closing liftgate

Closing request is present

Function sequence for closing liftgate

The liftgate control unit reads in the closing request from the interior CAN and actuates the liftgate electric motor in the closing direction until the rear control unit recognizes that the liftgate has engaged in the rotary tumbler on the liftgate lock. The rear control unit transmits the status of the liftgate rotary tumbler switch to liftgate control unit via the interior CAN. Then the liftgate control unit switches off the liftgate control electric motor.

The speed with which the liftgate is closed, is reduced momentarily before reaching the upper limit stop. For this purpose the liftgate control unit evaluates the signals from the liftgate control Hall sensor and the liftgate control position sensor.

Now the rear control unit actuates the liftgate central locking motor. It actuates the locking pawl in the liftgate lock and blocks the rotary tumbler. Then the rear control unit actuates the liftgate lock element (power closing). The liftgate is now completely closed.

If the liftgate is closed as a result of the request via the driver trunk lid/liftgate control button or the open/close liftgate button on the transmitter key, the liftgate control unit actuates the liftgate control warning buzzer 2 times during the liftgate movement. A warning tone does not sound when the request comes from the liftgate control button.

Function sequence for synchronizing liftgate

The liftgate control must be normalized after replacing the liftgate control drive unit or after adjustment work on the liftgate.

Normalization is the basis for assignment of the current position to the liftgate control unit position detected by the driver seat control unit. Normalization means learning in the upper and lower end positon of the liftgate (zero position).

Normalizing can be performed automatically and manually. In both cases the procedure must be started via the diagnosis tester.

Automatic normalization

When synchronizing automatically, the liftgate is opened in one cycle up to the upper end position. When the liftgate stands still for approx. t = 2 s, this position is learned in as the upper end position. Then the liftgate is completely closed at a constant speed until the locking pawl in the liftgate lock is locked. This position of the liftgate is learned as lower end position.

The liftgate control unit actuates the liftgate control electric motor accordingly.

Manual normalization

During manual normalization a complete cycle is run through. To normalize the upper end position, it is necessary to start automatic opening of the liftgate. When the liftgate recognizes when the end position (locked) is reached within the adjustable normalization range to be adjusted with the diagnosis tester, the liftgate control unit actuates the liftgate control electric motor for another t = 2 s and stores this position as the upper end position. Then the liftgate control unit switches off the liftgate control electric motor, even when the request is still present.

If an obstacle is recognized outside the normalizing limits during the normalization procedure, the liftgate control unit switches off the liftgate control electric motor.

To normalize the upper end position, it is necessary to start automatic closing of the liftgate. Then the liftgate control unit actuates the electric liftgate control motor in the closing direction until the rear control unit recognizes when the liftgate arrests in the rotary tumbler in the liftgate lock. If the liftgate is now within the normalizing limits for the lower end position and the liftgate control position sensor supplies a plausible value, the value read in after reaching the locking pawl by the liftgate control position sensor is set as the lower end position.

If an obstacle is recognized outside the normalizing limits during the normalization procedure, the liftgate control unit switches off the liftgate control electric motor. In this case it is necessary to renormalize. During the normalization procedure, the opening angle limitation is deactivated.

Function sequence for opening angle limitation

If required, the opening angle of the liftgate can be changed to prevent damaging the liftgate when extending objects are transported (skibox, surfboard, etc.).

First open liftgate to desired position to active opening angle limitation function. This can be accomplished manually or automatically via the liftgate control.

Manual

After the liftgate is opened manually to the desired position, press liftgate control button for approx. t = 2 s.

Automatic

If the liftgate is opened via the liftgate control, it is necessary to quickly press the liftgate control button once as soon as the liftgate is in the desired position. The liftgate remains in this position. An upright drive is required for activation of the opening angle limitation function.

Then press liftgate control button for approx. t = 2 s. The liftgate control unit reads in actuation of the liftgate control button via the interior CAN, switches off the liftgate control electric motor and stores the current position of the liftgate as upper opening angle limitation. For this purpose the liftgate control unit evaluates the signals from the liftgate position sensor.

Successful storage of the value for the opening angle limitation is confirmed by outputting a warning tone over the liftgate control warning buzzer. For this purpose the liftgate control unit directly actuates the liftgate control warning buzzer.

When the liftgate is opened, it is only opened to this stored position. The opening angle can be limited up to max. s = 20 cm in front of the upper end position of the liftgate.

The liftgate can be opened manually beyond the stored position. To deactivate the opening angle limitation, actuate liftgate control button for t = 2 s (any liftgate position). The end of the opening angle limitation function is confirmed acoustically via the liftgate control warning buzzer (double tone).

Function sequence for obstacle detection

To recognize pinching of lock-up during the opening and locking procedure of the liftgate, the liftgate control unit evaluates the following parameters:

Power consumption of liftgate control electric motor (obstacle recognized by power increase)
Motion speed of liftgate via liftgate control Hall sensor and liftgate control position sensor (obstacle recognizes by speed changes)
Resistance of anti-pinch protection contact strips (pinching recognized by contact between interior conductors)

The anti-pinch protection contact strips are located on the left and right at the liftgate stop strip. The system recognizes when the pinch protection contact strip has been touched (contact with the internal conductor) by a change in the resistance.

If the liftgate control unit recognizes pinching or lock-up while closing, the liftgate control electric motor is reversed and the liftgate is moved back to the initial position.

During opening the liftgate control electric motor is switched off and the liftgate remains in the momentary position.

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