Mercedes-Benz C-Class with New 4MATIC

• Greater efficiency with compact design and low weight
• Integrated multi-disc clutch for improved traction on ice and snow
• Interaction with ESP® and 4ETS electronic traction system

Exemplary passenger protection, superior driving safety, sporting agility and first-class comfort – since its launch in the spring of 2007 the new C-Class series has been scoring top points in these categories. Mercedes-Benz brings the good drive characteristics of saloon and estate cars to perfection with a complete, newly developed all-wheel-drive system, which has for years been a benchmark in design and engineering in the field of drive technology: 4MATIC.

The permanent all-wheel-drive system – available for the six-cylinder C 280, C 350 and C 320 CDI models – works together with the standard ESP® Electronic Stability Program, showing its strengths not only during adverse weather conditions such as rain, snow or ice but also when pulling away, accelerating, taking bends quickly or on poor road surfaces. In such conditions the electronically controlled all-wheel-drive offers even more driving stability, helping the driver to handle the car better in borderline situations. In addition, the 4MATIC provides extra traction when towing a trailer.

In the new 4MATIC models in the C-Class, these exemplary drive characteristics go hand in hand with classic Mercedes-Benz comfort. This is guaranteed, on the one hand, by the complex designs of the front and rear axle and the AGILITY CONTROL package with selective shock absorber control and, on the other, by the careful tuning of springs and shock absorbers of the all-wheel-drive models, which essentially correspond to the settings of rear-wheel-drive models. A further advantage of the 4MATIC in terms of comfort is the absence of conventional differential locks, which influence steering and handling in other all-wheel-drive cars.

Distributor gearbox integrated in the 7G-TRONIC automatic transmission

The latest-generation 4MATIC developed by Mercedes-Benz features a low additional weight of only 60 to 70 kilograms (depending on the model) and a compact design with significantly less installation space to the side in the area of the distributor gearbox. This requires no modifications to the body-in-white and passenger foot space is not restricted. The compact construction also contributes to further improvements in noise and vibration behaviour. Further assets include higher efficiency to achieve consumption targets, an improved power density in the drive train components and excellent torque and performance capacity.

Unlike before, the distributor gearbox is directly integrated in the 7G-TRONIC. The distributor gearbox consists of a centre differential of planetary design and two bevel gears, which form the side output to the front axle. The centre differential produces the newly defined torque distribution of 45 to 55 percent between front and rear axle (previously: 40 to 60 percent) which, in comparison to preceding models, can mainly be appreciated by even better driving stability and traction.

In the centre differential a so-called planet carrier takes over the output to the rear axle, whilst the sun wheel ensures torque transmission via power take-off to the front axle.

The split according to which the torque is distributed from the main gearbox depends on the ratio of cogs in the crown and sun wheel in the planetary differential: when driving straight ahead the drive and output shafts of the planetary gear set turn at the same speed. It is only when there is a difference in rotational speed in the wheels on the front and rear axle (when cornering, for instance) that a relative movement between sun wheel and planet carrier occurs to produce the balance in rotational speed. The teeth on the gear wheels in the planetary differential are angled in order to keep the noise level low.

Improved power take-off for even higher efficiency

An additional feature of this new drive train concept is the very compact side output to the front-axle transmission. It works in one stage, saving on an entire gear wheel stage in comparison with the previous 4MATIC drive system. In addition, the rear universal joint of the propeller shaft is integrated in the output gear wheel of the power take-off. This space-saving design makes it possible to guide the propeller shaft to the front axle very close to the gearbox without requiring any changes to the body-in-white.

The significantly higher efficiency of the new 4MATIC drive system, and the resulting decrease in fuel consumption compared to its predecessor, is based to a large extent on the omission of the gear wheel stage in the power take-off of the distributor gearbox and on an even more improved oil supply. The integrated design means that the main and distributor gearboxes have a joint oil supply. Around 100 millilitres per minute of fresh oil flow into the distributor gearbox through an additional branch in the external gearbox oil feed. As a result of the continual flow of oil, there is a build-up of oil in the chamber of the power take-off unit, which is constantly monitored and regulated.

The integrated design of the distributor gearbox also contributes to the high natural bending frequency of the engine-gearbox assembly, significantly improving the noise and vibration behaviour of the drive train. Thus, combined with a similarly improved bearing assembly, Mercedes-Benz engineers achieved a level of noise in the vehicle’s interior comparable with that of two-wheel-drive models in all conditions.

Multi-disc clutch with lock between front and rear axle

The double-disc clutch adjusted to the central differential is an innovative feature of the new Mercedes-Benz all-wheel-drive system. It is linked between the sun wheel and the crown wheel to produce a basic locking force of approx. 50 newton metres between the front and rear axle. The operational principle: the disc package is pre-loaded with permanent force by means of a disc spring. During wheelspin on one of the two axles, friction torque is transferred by the relative movement of the discs from the faster rotating axle to the slower rotating one.

This principle of varia­ble torque displacement between the front and rear axle produces significant improvements in traction and driving stability in 4MATIC models. Traction support produced by the double-disc clutch is particularly noticeable when the friction ratio between tyres and road surface is low, because the clutch automatically disables the drive train during a moderate starting process at a friction value between tyres and road surface of less than µ = 0.3 (more or less equivalent to snow). The wheels are prevented from rotating in such a way as to prevent the so-called “polish effect”, which leads to a reduction in friction value. Another advantage of the double-disc clutch can be seen in the further improved load-changing behaviour of the 4MATIC models.

The front axle gearbox of the 4MATIC models is a one-stage differential gearbox with fuel economy technology. This means its features include low-loss bearings, smooth running oil, and maximum efficiency gearing. The oil reservoir and the right engine support are screwed on to the front axle gearbox in the form of a “hang-on unit“. To transfer torque from the front axle gearbox to the left front axle shaft, a countershaft is guided through a moulded cast-iron shaft channel in the oil reservoir. The right axle shaft is directly linked to the front axle gearbox by means of connector gearteeth.

The one-stage design of the distributor gearbox means that the ring gear of the front axle gearbox can be positioned on the engine side. This new arrangement of the axle gearbox components creates sufficient space to place the front engine bearings directly over the axle shafts instead of in front of the axle shaft universal joints, as in the preceding model. The design of the newly developed all-wheel-drive specific engine supports is equally compact and firm, having a positive influence on noise and vibration behaviour.