For many years, 4MATIC has been Mercedes-Benz’s designation for its all-wheel drive models, from the C- to the CL-Class and of course its ever-growing portfolio of SUVs.Despite the common name, the German manufacturer offered no less than four different AWD systems, depending on the model and its customers’ needs – i.e., a G-Wagen has a different system than a CLS.
Now, Mercedes has announced details of a fifth 4MATIC system for the upcoming CLA compact sports saloon and its AMG-fettled performance version, the CLA 45 AMG, which it says, is “a completely new development tailored to the requirements of models with front-wheel drive”.
The new AWD system can be combined only with the 7G-DCT seven-speed dual clutch semi-auto transmission. A compact power take-off unit (PTU) that’s integrated in the transmission using the same lubrication system, resulting in less friction and a 25 percent weight saving over rival systems, provides power delivery to the rear axle.
Torque distribution is taken care by an electro-hydraulically activated multi-disk clutch integrated in the rear axle. Under normal driving conditions, the clutch is open and the car is almost 100 percent front-wheel drive for maximum fuel efficiency.
A rotor pump that’s also integrated in the rear-axle gear unit is automatically activated when an ESP-controlled valve detects minimal speed differences between the front and rear axles.
In milliseconds, the system pressure builds up and activates the rear clutch, which shifts torque between the two axles according to grip (torque-on-demand).
The way torque is distributed depends on which of the transmission’s program is selected. For example, in ECO mode, less torque is transferred to the rear for better fuel economy, while in SPORT and MANUAL, activation times are quicker and more torque is directed to the rear for more sporting handling, while in the 350HP CLA 45 AMG, it adapts according to the settings of the three-stage ESP.
By Andrew Tsaousis
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