The permanent all-wheel-drive system 4MATIC: More traction and high efficiency

Jun 23, 2014
The Mercedes-Benz 4MATIC drive system is one of the best-performing all-wheel-drive systems available; the control systems are groundbreaking. The basic design concept, with the engine installed longitudinally and the integral transmission and transfer case unit, produces a compact, lightweight arrangement that minimises frictional losses, heralding a number of benefits compared to other systems. Fuel consumption, for instance, is on a par with that of an equivalent vehicle with conventional drive system.
In cooperation with the dynamic handling control systems ESP®, acceleration skid control ASR and 4ETS, the basic 45:55 percent torque split between the front and rear axle ensures assured and predictable handling. When fine-tuning the control systems the engineers at the Mercedes-Benz Technology Centre placed particular importance on defined understeer characteristics. This is displayed even in the most varied of road conditions: on dry roads, in rain, in snow, on ice or on unsurfaced roads.
A double-disc clutch achieving a basic locking torque of approximately 50 Nm between the front and rear axle is fitted to the central differential. The clutch pack is permanently preloaded via a plate spring. In the case of spinning wheels on one of the two axles, a friction torque is transmitted to the axle spinning more slowly by relative movement of the discs. A sustained improvement to traction and directional stability of the vehicle are achieved through this principle of variable torque shift. Particularly in the case of low coefficients of friction between the tyres and the road surface the traction and stabilising effect of this so-called pre-lock clutch is clearly noticeable.
One stand-out feature of the 4MATIC all-wheel-drive system is the extremely compact design of the transfer case and the lateral output to the front axle. The rear universal joint of the propshaft to the front axle is integrated in the transfer case's output gear, meaning that the transmission requires far less sideways space. In addition to reducing weight and improving fuel consumption, this means that the transmission tunnel can be kept very narrow. Consequently the level of legroom in the vehicle interior is the same as for the models with rear-wheel drive. The compact design also increases the natural bending frequency of the engine/transmission assembly, which has a positive effect on NVH and quiet-running.