Basic Function Of Automatically Controlled All-Wheel Drive - GF28.00-D-9900A

Model All (Light transporter) 

Overview 

This document contains information on:

• General 
• Function 

General 

In contrast to the front or rear wheel drive, the drive force is forwarded to all wheels on all-wheel drive. The distributed driving power results in higher traction and higher lateral stability at the wheels.

Function 

In contrast to the engageable all-wheel system with fixed force distribution, the automatically controlled all-wheel drive is usually a permanent all-wheel drive with fixed or variable force distribution.

Whereas the all-wheel system with fixed force distribution in 4x4 mode directs e.g. 35 % of the torque to the front axle and 65 % to the rear axle, the all-wheel system with variable force distribution can distribute drive torques fully variably between the front and rear axle, according to the situation and without any intervention on the part of the driver ("torque on demand").

On vehicles with 4MATIC all-wheel system and variable force distribution, an electronically regulated multiplate clutch integrated into the transfer case provides for the torque distribution. If the multiplate clutch is open during normal driving operation, only the rear axle drives the vehicle. If the clutch is closed, the front axle comes into play. This distribution ensures that the system provides high traction according to the situation.

The greatest advantage of a multiplate clutch is that it can be shifted under load. This means that it makes no difference if the vehicle is being driven on uneven terrain or around curves. The "torque on demand" system always distributes the drive torque so that the vehicle stabilizes automatically.

Further advantage compared to the shift-on-the-fly four wheel drive: In addition to increased comfort through the automatic torque distribution, the system is significantly quieter during operation. As soon as the driving situation requires it, the drive torque is directed to the front axle. If this is no longer required - for example, during strong braking maneuvers with ABS intervention - the front drivetrain is switched off and the torque is reduced to zero. In the event of imminent understeering or oversteering under load, the drive torque is initially distributed so that the vehicle stabilizes. Only if these measures do not lead to easing do the ESP® (Electronic Stability Program) and ETS (Electronic Traction System) management systems that have been adapted to the 4x4 system then engage. Active-selective brake application takes over the function of the differential lock and vehicle dynamics control.

	Additional basic functions
	Basic function of all-wheel drive with automatic transmission	Model all with transmission 725.0 as of model year 2021 with code A4M (4MATIC)	GF28.00-D-1001A