Interaxle Differential Lock, Function - GF28.60-P-3100VGF
MODEL 166 with TRANSMISSION 725.0 as of model year 2016 with CODE 430 (On & off-road package)
Sectional view of transfer case from left front
Sectional view of transfer case from left rear
Function requirements for interaxle differential lock, general
- Ignition ON
- Drive position engaged
Interaxle differential lock, general
Actuating the interaxle differential lock prevents the drive torque of the center differential from being equally distributed for front and rear axle. Corresponding to the locking ratio of the interaxle differential lock and the road surface condition (skid torque), the drive torque is shifted between the axles.
Interaxle differential lock, function sequence
The function sequence is subdivided into the following steps:
- Transmission mode selection, function sequence
- Lock control, function sequence
- Safety concept, function sequence
- Slip-dependent lock control, function sequence
- Function sequence for lock actuation with anti-lock braking system (ABS)/Electronic Stability Program (ESP®) control
- Lock overload protection, function sequence
Transmission mode selection, function sequence
The driver can choose from six different transmission modes using the off-road package transmission mode controller (N72/3s1), which is located on the offroad control panel control unit (N72/3).
The "Individual", "Sport", "Comfort", "Slippery", "Off-road" and "Off-road+" transmission modes can be selected individually by turning the
- Specified locking torque, function sequence
off-road package transmission mode control. The active transmission mode is signaled to the driver by red light-emitting diodes (LED).
The individual transmission modes consist of various functions, options and settings of the individual systems.
| Position Off-Road package transmission mode controller | Feature | Suspension settings | Drive concept |
|---|---|---|---|
| Individual | - | - | - |
| Sport | Maximum vehicle dynamics | Lowered vehicle level, greater degree of leveling of roll stabilization, sporty steering characteristics | Shorter shift times, gear maintained at high lateral acceleration, revving up during gear range change, earlier downshifting, faster acceleration response when accelerator pedal is depressed, only "High" shifting permitted at transfer case |
| Comfort | - | - | - |
| Slippery conditions | High driving stability, systems adapted to operation with snow chains | Default | Flat accelerator pedal curve, start-off in 2nd gear range, increased engagement limits up to approx. 50 km/h (snow chains), ASR (acceleration skid control) controls on basis of traction on straight stretches and sensitively on bends |
| OFF-ROAD | Systems are designed for gentle off-road conditions (dirt tracks, gravel, sand) | Torsion-oriented setting of roll stabilization, raised vehicle level (Offroad level 1) | Delayed engine torque reduction, gearshift operations takes place at higher engine speed, flat accelerator pedal curve |
| Off-road+ | Systems are configured for severe off-road conditions (rocks, steep terrain) | Torsion-oriented setting of roll stabilization, optimized for active torsion, extreme increase in vehicle level (Offroad level 2) | DSR (D ownhill-S peed-R egulation) active if this mode is selected, flat accelerator pedal curve |
Specified locking torque, function sequence
When the lock is actuated, the transfer case control unit (N15/7) calculates a specified locking power depending on the current operating condition and the selected transmission mode.
To allow pre-control of the locking torque, the transfer case control unit requires the following information:
- Vehicle speed
- Engine torque
- Accelerator pedal position
- Cornering recognition
- Wheel speeds
Lock control, function sequence
The interaxle differential lock regulates the distribution of the engine torque between the front and rear axles.
The transfer case control unit actuates the transfer case switchover magnet. The transfer case switchover magnet switches between the "High/Low shift" function and the "Interaxle differential lock" function. When the transfer case actuator motor is actuated by the transfer case control unit, the transfer case actuator motor turns the lock control disk (9).
Turning of the lock control disk (9) produces a contrarotation of the front and rear lock levers (10, 11). As the lock levers (10, 11) turn, the balls (2) in the ball ramp mechanism run up the ball ramps (1), producing an axial movement of the rear lock lever (11). This causes an axial displacement of the shift lock (3). This axial displacement produces a defined friction torque in the disk pack (5). The differential housing (7) and the front differential side gear (8) are mutually locked.
Safety concept, function sequence
In the deenergized state (power failure), the transfer case switchover magnet interrupts the connection between the transfer case actuator motor and the front and rear lock levers (10, 11) and the disk pack (5) is pushed back to the starting position by the disk spring pack (4).
Slip-dependent lock control, function sequence
While lock control is active, the transfer case control unit, in combination with the pre-control, calculates a suitable range for the slip threshold and the optimum locking torque in order to avoid oversteer and understeer under load. For this the transfer case control unit requires the following information:
- Vehicle speed
- Engine torque
- Cornering recognition
- Tire tolerances
- Wheel speeds
Function sequence for lock actuation with anti-lock braking system (ABS)/Electronic Stability Program (ESP®) control
The transfer case control unit must take into account the requirements of the ABS and ESP® systems in order to avoid negative influences on driving stability. For this purpose the transfer case control unit is capable of opening the interaxle differential lock.
To guarantee this function, the following information is required:
- Stop light signal
- Deceleration at the rear axle
- Vehicle speed
- ABS request
- ESP® request
Lock overload protection, function sequence
The aim of the lock overload protection is to protect the interaxle differential lock against damage and guarantee the maximum possible availability of the lock function.
After ignition "OFF/ON", the transmission mode last selected (with the exception of "Sport" transmission mode) is active. Transmission mode "Comfort" is automatically set by default in transmission mode "Sport" after ignition "OFF/ON".
| Overview of system components, transfer case (VG) | GF28.10-P-9998VGF |