Pic. 6.24. 4Matic transmission diagram: 1 - cardan shaft (to rear axle differential); 2 - transfer case; 3 - gearbox with spur gear for the front axle; 4 - cardan shaft (to front axle differential); 5 – front axle differential; 6 - front wheel drive shaft
All-wheel drive in the new version of 4Matic is via a permanently connected 2-speed single-speed transfer case (pic. 6.24) only mechanically with a constant torque distribution in the ratio: 65% to the rear axle and 35% to the front axle.
The function of torque alignment between the axles is performed by a central differential with a double planetary mechanism. Drive to the front wheels is provided by a spur gear reducer with enhanced noise reduction that also acts as an oil pump and supplies the transfer case lubrication system.
The differential lock function is performed by the ETS electronic traction control system, which regulates the amount of torque on individual wheels, reducing it by braking and at the same time increasing traction on the other wheels.
Added to this is the electronic stability program ESP, proven on other Mercedes models, which on 4Matic models controls all four wheels when sensors detect a critical situation of wheel adhesion to the road - for example, when cornering or when overtaking on slippery surfaces.
In addition, the so-called Brake-Assist system is also integrated into this comprehensive control system (BAS), which since 1997 has been serially installed on all model lines of Mercedes cars. Here we are talking about control in situations of emergency braking. Harsh braking in a critical case is evaluated by an electronic device by the speed of pressing the pedal. From this point on, the electronics take over control to ensure the most efficient braking until the driver begins to control the effort on the pedals (see also section «Brake system»).
Diagnosis and troubleshooting of ETS, ESP and BAS systems is in any case the lot of specialists. Even the usual oil change in the transfer case and front axle differential is no longer necessary. Both units use a lifetime operating fluid.