The 4×4 family from Mercedes-Benz currently comprises more than 60 models. The A, B and CLA-Class are now all optionally available with the new generation of the 4MATIC permanent all-wheel-drive system featuring fully variable torque distribution. In addition, from March 2014 the new GLA will be joining the Mercedes-Benz SUV model range.
The most innovative components of the new 4MATIC include the power take-off to the rear axle, which is integrated into the 7G-DCT automated dual clutch transmission, and the rear-axle gear unit with integrated, hydraulically actuated multi-disc clutch. This set-up allows fully variable distribution of the drive torque between the front and rear axles. Additional benefits of this design are a lower system weight compared with the competition and also high efficiency. As with their front-wheel-drive counterparts, all 4MATIC models also boast good energy efficiency.
Even the best all-wheel drive is no substitute for winter tyres
Like any other all-wheel drive system, the 4MATIC versions have to abide by the laws of driving physics. The fundamental rule is that a tyre is only able to transfer a certain level of overall force to the road surface. If a particularly high degree of longitudinal force is required during acceleration or braking, for example, the available lateral force is reduced. When cornering, the reverse applies: now a large amount of lateral force is required to keep the vehicle on course, while the longitudinal force potential is restricted. The engineers’ skill in designing the drive mechanism and fine-tuning the control systems lies in their ability to exploit these correlations in such a way as to ensure the best possible handling characteristics under all conditions. The frictional coefficient µ describes the physical grip between the tyres and the ground. This figure is high on a dry road (µ = 0.9) and low on a snow-covered road (µ = 0.3).
Source: Daimler AG