Overview
This document contains information on:
General
Function
General
The transfer case with front axle transmission output is responsible for distributing the torque delivered by the automatic transmission to the rear and front axles.
All-wheel drive increases the number of driven wheels, thus improving tire-to-road adhesion. Also, slip is reduced and the driving power is distributed to all of the wheels. The distributed driving power results in higher traction and higher lateral stability at the driven wheels. The torque split is either fixed or variable, depending on the transfer case. The ratio of the transfer case is 1:1. In addition, a modified accelerator pedal curve in the combustion engine control unit and the off-road ABS function in the ESP® control unit are also activated.
Example illustration of transfer case (ON&OFF-ROAD Package) |
1 | Primary shaft sprocket |
2 | Primary shaft |
3 | Sun gears |
4 | Planetary gears |
5 | Rear axle output flange |
6 | Front axle output flange |
P28.10-2270-82
Function
ON&OFF-ROAD package
The ON&OFF-ROAD Package provides permanent all-wheel drive with a locking differential (transfer case) and two open differentials (front and rear axles). The torque split of 50:50 between the front and rear axle is specified as a fixed value in the transfer case for an open interaxle differential lock clutch pack. The Low/High function in the transfer case can be used to select two ratios. The "High" on-road ratio is 1:1, and the "Low" off-road reduction is 2.93:1. The differential lock in the transfer case can be actuated using the OFF-ROAD Package drive program switch.
A distinction is made between the following 3 transfer cases:
Transfer case with fixed drive ratio
This transfer case has no locking mechanism and has a fixed drive ratio of 50:50. Spinning wheels are braked via an intervention at the relevant wheel.
Transfer case with electronically controlled multiplate clutch |
1 | Primary shaft sprocket |
2 | Primary shaft |
5 | Rear axle output flange |
6 | Front axle output flange |
7 | Interaxle differential lock disk pack |
8 | Transfer case control unit |
P28.10-A019-82
Transfer case with electronically controlled multiplate clutch
This transfer case has an electronically controlled multiplate clutch for distributing the drive torque variably between the axles. The drive torque is transmitted directly to the rear axle by means of a continuous main shaft. An electric actuator motor increases the pressure on the multiplate clutch via a ball ramp and a lever mechanism and thus also transfers the drive torque to the front axle. In addition, the transfer case with electronically regulated multiplate clutch has a lever mechanism for changing the contact pressure on the multiplate clutch for the 0-100 % variable torque distribution.
Sectional view of transfer case with additional auxiliary gearset |
1 | Primary shaft sprocket |
2 | Primary shaft |
5 | Rear axle output flange |
6 | Front axle output flange |
7 | Interaxle differential lock disk pack |
8 | Transfer case control unit |
9 | Ball ramp |
10 | Transfer case absolute sensor |
11 | Actuator shaft |
12 | Planetary gear system for step-down ratio |
13 | Electric motor |
14 | Worm shaft |
15 | Sliding sleeve |
P28.10-A020-76
Transfer case with additional auxiliary gearset
This transfer case has an electronically controlled multiplate clutch for distributing the drive torque variably between the axles. In addition, the transfer case has an auxiliary gearset and an automatic locking effect of 0-100 % for off-road operation.
The drive torque is transferred directly to the rear axle via a continuous transmission output shaft. Via a ball ramp and a lever mechanism, an actuator motor moves a ring which changes the pressure on the multiplate clutch, thus shifting the entire drive torque.
In the design with additional auxiliary gearset, a planetary gear set is also used. Synchronized shifting ability from the step-down ratio is permitted up to a maximum vehicle speed of 70 km/h. Unsynchronized shifting to the step-down ratio may only be performed while the vehicle is stationary.
A sliding sleeve is used to couple the planetary gear system for the step-down ratio.
Example illustration of transfer case oil cooling |
16 | Low-temperature circuit |
17 | Coolant feed to transmission oil heat exchanger |
18 | Coolant feed to heat exchanger of transfer case |
19 | Coolant return to coolant circuit |
20 | Automatic transmission fluid feed to transmission oil heat exchanger |
21 | Return line for automatic transmission fluid from transmission oil heat exchanger |
22 | Coolant return to coolant circuit |
A | Heated transmission oil or coolant |
B | Cooled transmission oil or coolant |
P27.55-A017-76
Cooling
Oil cooling is regulated as required to keep the transfer case operating temperature constant in a temperature range adapted to the corresponding operating status.
Oil cooling lowers the temperature of the transmission oil, which in turn prevents any overheating damage to the transfer case.
Function schematics | |||
Function schematic for transfer case control | Model all with transmission 725.0/1 with code 430 (On & off-road package) with code M005 (Vehicles with 4MATIC/all-wheel drive) | ||
Additional base function | |||
Transfer case oil supply, basic function | Model all with transmission 725.0/1 |