"Low/High" shift, function - GF28.60-P-1000GZ
MODEL 164.1 with CODE (430) Offroad package
MODEL 164.8 with CODE (430) Offroad package
On-road ratio "High"
The driver can use the Low Range switch (N72s31), which is located in the lower control panel control unit (N72), to switch from the on-road ratio "High" to the offroad ratio "Low".
When the Low Range switch is pressed, the transfer case control unit (N15/7) shifts the gear ratio in relation to:
- Vehicle speed
- Transmission in position "N"
- Position of transfer case motor
- Additional CAN signals
Shifting the on-road ratio
The following 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 when 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 switch 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 onroad ratio gearing (2). If the sliding sleeve is connected with the on-road ratio gearing of the differential housing (5), the ring gear (6) (via the sliding sleeve) and the planetary gears (4) (via the planetary gear shafts (1)) are fixed in relation to the differential housing after synchronization. The planetary gear set rotates as a unit with a ratio of 1:1.
Preselection function
If the driver presses the Low Range switch while the function requirements are not satisfied, the LED in the Low Range switch flashes. When the function requirements are satisfied, the ratio in the transfer case changes. If the Low Range switch 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.
Offroad ratio "Low"
Shifting the offroad ratio
The following 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 when reversing < 10 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 "High" to "Low". A red LED integrated in the Low Range switch 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 offroad ratio gearing (9). The offroad ratio gearing is fixed in relation to the synchronizer ring (12) and the synchronizer spring (11) on the rear transmission housing (10). After synchronization the ring gear (via the sliding sleeve) is connected with the offroad ratio gearing and with the rear transmission housing. This results in a ratio of 2.93:1.
Preselection function
If the driver presses the Low Range switch while the function requirements are not satisfied, the LED in the Low Range switch flashes. When the function requirements are satisfied, the ratio in the transfer case changes.
If the Low Range switch 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 in the instrument cluster if necessary.
Safety concept
The following safety functions exist to prevent damage in the drivetrain when shifting from "High" to "Low" (offroad ratio) or from "Low" to "High" (on-road ratio):
- If drive position "D" is engaged during the shift operation, the electric control unit (VGS) (Y3/8) 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.
| Transfer case control unit, component description | N15/7 | GF28.19-P-3200GZ |
| Transfer case absolute sensor, component description | B57 | GF28.19-P-3201GZ |
| Transfer case actuator motor, component description | M46/2 | GF28.19-P-3202GZ |
| Transfer case switchover magnet, component description | Y108 | GF28.19-P-3203GZ |
| Differential, component description | GF28.50-P-1000GZ | |
| Planetary gear set, component description | GF28.50-P-1200GZ |