Mercedes-Benz C-Class with New 4MATIC

Better traction and driving stability

Four wheel drive may not be as big of an asset for everybody, but with most of the WCF crew living in Helsinki, Finland, one of the most northern capital cities in the world, it is a big topic.

Mercedes is launching their new 4MATIC permanent all-wheel-drive system on the new C280, C350 and C320 CDI. And where the previous generation was praised for its design and engineering, the new generation is more efficient and weighs less (60 to 70 kg depending on the model), where weight tends to be the biggest drawback of AWD systems.

The new AWD system is based on a transfer case with a centre differential, integrated into seven-speed 7G-TRONIC automatic transmission which delivers power in a 45:55 ratio to the front and rear axles.

The 4MATIC is paired with ESP (Electronic Stability Program) and 4ETS traction system, giving the new 4MATIC better traction on slippery surfaces. The 4ETS does the same as conventional differential locks but with greater comfort.

Read on for full details on the new generation 4MATIC system.

Press Release

• 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.

Electronic traction system instead of differential lock

Rather than conventional differential locking systems, the 4MATIC uses the electronically controlled 4ETS traction system, an additional component of the ESP® Electronic Stability Program. This has also been further developed and now has improved traction with higher levels of comfort. 4ETS is automatically activated if one or more wheels lose their grip on the road surface. In such cases 4ETS automatically applies the brakes to these wheels individually and thus simultaneously increases drive torque to the wheels with sufficient traction. These thousandth-of-a-second braking impulses achieve three differential locks:

1. Rear axle: If one wheel is caught in wheelspin, the braking system is applied and transfers torque force equivalent to the braking force to the other rear wheel. This fulfils the function of a rear lock.

2. Front axle: The same principle as the rear axle applies to the front wheels, so that 4ETS also replaces the front lock.

3. Central lock: If both rear axle wheels are caught in wheelspin, the braking system is applied to them simultaneously, whilst the 4MATIC distributor gearbox balances out the difference in rotational speed between front and rear axle. In this way 4ETS fulfils the role of a central differential lock.

In addition, the automatic braking impulses of the 4ETS system adjust to the speed of the car:

• At low speeds braking intervention is possible in all wheels. Thus, 4ETS achieves the effect of three locks and provides maximum traction.
• At medium speeds braking pressure is restricted to the wheel not caught in wheelspin so as not to compromise driving stability. Should both rear wheels lose their grip on the road surface, the braking system is applied to them simultaneously – at this speed, stability has priority over traction.
• At high speeds 4ETS controls braking pressure on both rear wheels synchronously – even when only one of the rear wheels is caught in wheelspin. At the same time the system does without braking intervention on the rear axle, in order to achieve the best possible driving stability.

Within the context of the development of the traction system and of acceleration skid control (ASR), Mercedes-Benz engineers have fine-tuned the controls so that specific situations – such as one-sided wheelspin when pulling away – are more easily detected. The aim was to further increase acceleration with minimal wheel slip. Acceleration skid control depends on the particular driving situation and, for example, lowers the thresholds for the regulation of engine torque in bends on a smooth road surface in order to ensure the stability of the vehicle. On the other hand, the system can reduce control thresholds for the braking impulses when taking bends on a dry road surface. In this way a good balance between the best possible traction and high driving stability is achieved in any driving situation.

As with all driving safety systems from Mercedes-Benz, the 4MATIC notifies the car driver as soon as he is approaching the limits. In such cases a yellow warning light appears in the instrument cluster. This is an unmistakable signal that driving must be adapted to the road conditions.

4MATIC in combination with high-torque V6 engines

The newly developed 4MATIC drive system combines Mercedes-Benz C-Class motors with high-torque V6 engines:

• Models C 280 4MATIC, C 350 4MATIC and C 320 CDI 4MATIC are available in saloons.
• The permanent all-wheel-drive system is available with the six-cylinder diesel engine in the estate model.

The main technical data at a glance:

	C 320 CDI 4MATIC saloon and estate	C 280 4MATIC saloon	C 350 4MATIC saloon
Displacement cm³	2987	2996	3498
Output kW/hp	165/224	170/231	200/272
Max. torque Nm	510 at 1600-2800/min	300 at 2500-5000/min	350 at 2400-5000/min
0-100 km/h s	6.7 (saloon) 7.1 (estate)	7.3	6.3
Comb. fuel consumption l/100 km	7.7 – 8.0 (saloon)7.8 – 8.1 (estate)	9.4 – 9.6	10.0 – 10.3

The newly developed, more efficient all-wheel-drive system reduces fuel consumption in the 4MATIC models in the C-Class by up to 0.5 litres per 100 kilometres. Depending on the motorization, additional all-wheel-drive fuel consumption drops by between 0.2 and 0.4 litres per 100 kilometres. The V6 engines have been modified for use in the 4MATIC models. The changes relate mainly to the oil circulation system, which needs an oil vacuum hose, an oil guard, an oil level meter tube, a fuel level plunger and a newly designed oil reservoir with integrated shaft channel. A countershaft is fed through this channel, linking the front axle gearbox with the drive shaft of the left front wheel.

The integral supports, to which the engine, front axle and steering assembly are fixed, have also been further developed for the 4MATIC models and, in spite of limited space, meet the same specifications as rear-wheel-drive vehicles. The integral support of the 4MATIC versions consists of several parts, each with a different material composition, designed to meet high demands from

Mercedes-Benz in terms of safety and service life. The force transmission points of the front axle, steering assembly and engine, and the connecting parts of the integral support are specifically reinforced.

Front axle and braking system adapted

In the course of designing the 4MATIC chassis, Mercedes-Benz engineers have succeeded in achieving the same results in terms of agility and comfort as with the rear-wheel-drive C-Class models.

The three-link front axle was borrowed for the all-wheel-drive model and, for reasons of space, modified so as to enable the torsion bar stabiliser to be placed behind the centre of wheel. It is fixed to the integral support by means of special consoles. The position of the steering gear and the steering gear shaft also differs from that of the standard model, so the front axle kinematics have been recalculated and adjusted. The C-Class multi-link rear axle remains unaltered in the 4MATIC models.

Large, internally ventilated disc brakes on the front and rear axle come as standard on all 4MATIC C-Class models.

Data and dimensions of the braking system at a glance:

Front axle	C 280 4MATIC	C 350 4MATIC, C 320 CDI 4MATIC*
Brake calliper Piston diameter Brake disc Diameter Thickness	Floating calliper 60 mm Internally ventilated 295 mm 28 mm	Floating calliper 60 mm Internally ventilated 322 mm 32 mm
Rear axle
Brake calliper Piston diameter Brake disc Diameter Thickness	Floating calliper 38 mm Internally ventilated 300 mm 10 mm	Floating calliper 38 mm Internally ventilated 300 mm 22 mm

*saloon and estate