Transfer Case Control, Function - GF28.19-P-3000VGC
MODEL 166 with TRANSMISSION 722.9 up to model year 2016 with CODE 430 (On & off-road package)
Function requirements for transfer case control, general
- Ignition ON
- Gear range "N" engaged
Transfer case control, general
The electronically controlled transfer case combines the "High/Low shift" function and the differential lock (interaxle differential lock). The transfer case is actuated and monitored by the transfer case control unit (N15/7).
Transfer case control, function sequence
The function sequence is subdivided into the following steps:
- "High/Low shift" (on-road and off-road ratios), function sequence
- Signal course for "High/Low shift" (on-road and off-road ratio)
- Interaxle differential lock, function sequence
- Signal course for interaxle differential lock
"High/Low shift" (on-road and off-road ratios), function sequence
The transfer case is equipped with a planetary gear set which allows the driver to shift between the "High" on-road ratio and the "Low" reduction ratio by operating the Low Range button (N72s31) under certain shift conditions (High/Low< 40 km/h, Low/High< 70 km/h) while the vehicle is in motion. The planetary gear set is located in the central differential module. The "High" on-road ratio is 1:1, the "Low" off-road reduction ratio is 2.93:1. The reduction ratio allows the driver to drive extremely slowly off-road or when towing a trailer.
The transfer case control unit monitors and shifts the transfer case according to:
- Vehicle speed
- Position of transfer case actuator motor (M46/2)
- Additional CAN signals
If all the shift conditions are satisfied, the transfer case control unit actuates the transfer case actuator motor and the ratio in the transfer case is changed.
Signal course for "High/Low shift" (on-road and off-road ratio)
The required gear ratio is selected using the Low Range button, which is located in the center console on the lower control panel control unit (N72). The lower control panel control unit sends the signal to the center console switch-LIN (LIN B12) to the SAM control unit (N10). The data from the SAM control unit is routed via the interior CAN (CAN B), chassis CAN 1 (CAN E1) and drive train CAN (CAN C) to the transfer case control unit. The transfer case control unit changes the position of the transfer case actuator motor according to the request.
The "High/Low shift operation" takes place irrespective of the transmission mode selection. It is, however, not possible to shift to the transfer case position "Low" with the "Sport" transmission mode activated.
The transfer case absolute sensor (B57) registers the position of the "High/Low" shift fork in the transfer case and forwards the information to the transfer case control unit.
Interaxle differential lock, function sequence
The engine torque is distributed through the interaxle differential, with opened interaxle differential lock clutch pack, in equal amounts between front and rear axle. To ensure optimum torque distribution is achieved between the front and rear axle in every driving situation, the transfer case is equipped with an electronically-regulated interaxle differential lock. The transfer case control unit detects wheel slip and locks the interaxle differential by means of a multidisk clutch (interaxle differential lock) according to the driving situation. The transfer case control unit calculates an optimum locking power (pre-control) depending on the driving situation and the selected transmission mode. In order to avoid oversteer and understeer under load, a suitable slip range for the multidisk clutch (interaxle differential lock) is calculated in addition to the optimum locking torque. The interaxle differential lock is activated by the transfer case control unit via the transfer case switchover magnet (Y108) and the transfer case actuator motor.
For this the transfer case control unit requires the following information:
- Wheel speeds
- Engine torque
- Cornering recognition
- Tire tolerances
Furthermore, the transfer case control unit takes into account requirements of the anti-lock braking system (ABS) and Electronic Stability Program (ESP®) systems in order to avoid negative influences on braking stability. To guarantee functionality, the interaxle differential lock is opened when required by the ABS and ESP® systems.
For this purpose the following parameters are available to the transfer case control unit on the CAN bus:
- Stop light signal
- Deceleration at the rear axle
- Wheel speeds
- ABS request
- ESP® request
The lock overload protection guards the interaxle differential lock against damage and guarantees the maximum possible availability of the lock function.
Signal course for interaxle differential lock
The required transmission mode is selected via the off-road package transmission mode control (N72/3s1) which is located on the offroad control panel control unit (N72/3). The off-road operating panel control unit sends a signal over the center console switch LIN to the SAM control unit. The data from the SAM control unit is routed via the interior CAN, chassis CAN 1 and drive train CAN to the transfer case control unit. The interaxle differential lock is activated by means of actuation of the transfer case switchover magnet or transfer case actuator motor by the transfer case control unit.
View of indicators in instrument cluster (A1)
| Position Off-road package transmission mode controller: | Trailer | Snow | Sport | Auto | Offroad 1 | Offroad 2 |
|---|---|---|---|---|---|---|
| Operating state of subsystems: | ||||||
| Transmission mode "M" | - | - | - | - | - | - |
| Electronic Stability Program (ESP®) | ON | ON | ON | ON | ON | ON |
| Adaptive damping system (ADS) | Comfort | Comfort | Sport | Comfort | Comfort | Comfort |
| Level control | Normal | Normal | Sport | Normal | Stage 1 | Stage 2 |
| Downhill Speed Regulation | - | - | - | - | - | ON |
| "High/Low" position | Freely selectable | Freely selectable | High | Freely selectable | Freely selectable | Freely selectable |
| Electrical function schematic for transfer case control | PE28.19-P-2054-97NAA | ||
| Overview of system components, transfer case (VG) | GF28.10-P-9998VGC |