"Low/High" Shift Mechanism, Function - GF28.60-P-1000VGF
MODEL 166 with TRANSMISSION 725.0
as of model year 2016
with CODE 430 (On & off-road package)
Function requirements for "Low/High" shift, general
- Ignition ON
- Gear range "N" engaged
"Low/High" shift, general
The driver can shift from the "High" on-road ratio to the "Low" reduction ratio using the Low Range button (N72s31).
When the Low Range button is pressed, the transfer case control unit (N15/7) shifts the gear ratio in relation to:
- Vehicle speed
- Position of transfer case actuator motor (M46/2)
- Additional CAN signals
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.
"Low/High" shift, function sequence
The function sequence is subdivided into the following steps:
- Preselection function, function sequence
- Engage "High" on-road ratio, function sequence
- Engage "Low" reduction ratio, function sequence
- Safety concept, function sequence
Preselection function, function sequence
If the driver presses the Low Range button while the function requirements are not satisfied, the LED in the Low Range button flashes. When the function requirements are satisfied, the ratio in the transfer case changes. If the Low Range button is pressed a second time while the preselection function is active, the function is terminated. During the preselection time period, information and warning messages are displayed in the multifunction display (A1p13) in the instrument cluster (A1) if necessary.
Transfer case in "High" on-road ratio shift position
Engage "High" on-road ratio, function sequence
The following shift conditions must be satisfied before the transfer case control unit initiates the ratio change from "Low" to "High":
- Engine speed > 400 rpm
- Vehicle speed < 70 km/h
- Transmission in position "N"
- Vehicle speed while reversing < 20 km/h
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 from "Low" to "High". A red LED integrated in the Low Range button indicates the current operating state. When changing the gear ratio from "Low" to "High" the transfer case actuator motor moves the sliding sleeve (3) by the rotation of the motor shaft (8) via the shift fork (7) in the direction of the on-road ratio gearing (2). If the sliding sleeve (3) is connected with the on-road ratio gearing (2) of the differential housing (5), the ring gear (6) is fixed in place via the sliding sleeve (3) and the planetary gears (4) (via the planetary gear pins (1)) in relation to the differential housing (5) after synchronization. The planetary gear set rotates as a unit with a ratio of 1:1.
Transfer case in "Low" reduction ratio shift vposition
Engage "Low" reduction ratio, function sequence
The following shift conditions must be satisfied before the transfer case control unit initiates the ratio change from "High" to "Low":
- Engine speed > 400 rpm
- Vehicle speed <40 km/h
- Transmission in position "N"
- Vehicle speed during reverse travel < 10 km/h
- "Sport" transmission mode inactive
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 from "High" to "Low". A red LED integrated in the Low Range button indicates the current operating state. When changing the gear ratio from "High" to "Low" the transfer case actuator motor moves the sliding sleeve (3) by the rotation of the motor shaft (8) via the shift fork (7) in the direction of the reduction gearing (9). The reduction gearing (9) is fixed to the rear transmission housing (10) with the synchronizer ring (12) and the annular spring (11). After synchronization, the ring gear (6) (via the sliding sleeve (3)) is connected to the reduction gearing (9) and to the rear transmission housing (10). This results in a reduction ratio of 2.93:1.
If the "Sport" transmission mode is activated, it is not possible to shift to the "Low" reduction ratio.
Safety concept, function sequence
The following safety functions exist to prevent damage in the drivetrain when shifting from "High" to "Low" (reduction ratio) or from "Low" to "High" (on-road ratio):
- If gear range "D" is engaged during the shift operation, the fully integrated transmission control unit (Y3/8n4) is locked by the transfer case control unit.
- If a shift operation is attempted but fails to mesh (e.g. tooth to tooth), the attempt is repeated. If the shift operation cannot be completed, the ratio previously engaged is retained.
| Overview of system components, transfer case (VG) | GF28.10-P-9998VGF |