Make space for elegance: The new Mercedes-Benz E-Class Estate - PART VIII


Stuttgart, Germany, Oct 12, 2009

Chassis and suspension: Driving pleasure with a high level of comfort

- On a level: automatic self-levelling at the rear as standard
- Adaptable: adaptive damping control adjusts to the driving situation
- A pleasure to drive: additional brake functions such as HOLD and Hill-Start Assist

The newly developed DIRECT CONTROL suspension with standard-fit amplitude-dependent damping system in the new E-Class helps to ensure a high degree of long-distance comfort in the Estate too. In addition, the standard self-levelling rear suspension ensures that the Estate always remains at the same level, even when fully loaded. The suspension setup of the Estate has also been adapted to suit the modified body geometry, with slightly stiffer shock absorber settings and torsion bar stabilisers. Without any penalty in road roar and tyre vibration characteristics, this makes the Estate as agile as the Saloon.

The DIRECT CONTROL shock absorber system reduces the damping forces automatically when driving normally with low shock-absorber impulses, and increases the forces up to the maximum as required when cornering at speed or performing evasive manoeuvres.It is purely hydromechanical and requires no sensors or electronics. The core components are a bypass channel in the shock absorber's piston pin and a control piston moving within a separate oil chamber. When linear travel of the shock absorber is low, the control piston forces oil through the bypass channel to produce a significantly smaller damping force at the actual damper valve. The resulting, "softer" shock absorber characteristic translates into a high level of ride comfort. If the excitation of the shock absorber is greater, the control piston moves to its limit position so that oil ceases flowing through the bypass duct, meaning that the full damping force is available.

In the interests of favourable axle kinematics, superior vibrational comfort and improved safety, the lower link of the the three-link front suspension with McPherson struts consists of two separate elements which act as torque and cross struts. In addition to precise wheel location, this design has the particular advantage of compensating vibrations caused by tyre imbalances or fluctuating brake forces better than rigid wishbones. It also provides longer deformation paths in the event of a frontal collision. The third front-axle link is the track rod which connects the transversely installed steering gear to the wheels.

In order to further optimise ride comfort, the Mercedes experts have chosen a starkly upright position for the spring struts so as to reduce the forces acting on the torque strut bearing. As a consequence, it was possible to reduce the rigidity of the newly developed three-phase head bearings, which has a positive effect on the chassis' tyre/road contact characteristics and rolling characteristics – for example when driving over expansion joints running across the road. The specific use of aluminium and steel reduces the weight of the front axle by twelve percent compared to the previous model. The forwards-slanting torque struts and the cross struts are made of aluminium.

High-strength subframes for axle, steering, engine and transmission

The front-axle components, steering gear, engine and transmission are pre-mounted on a high-strength-steel subframe which is bolted securely to the body's side members, making it a key component in the front crash structure of the new E-Class: in the event of a frontal impact, the subframe forms a separate load-bearing path along which the impact energy is absorbed. The stiffness at the connecting points between the subframe and the body where load is transferred as a result of the forces and vibrations produced by the chassis and suspension has been increased substantially, all of which translates into more agile and more precise handling.

Steering: variable ratio for exceptional safety and agile handling

Standard equipment for the four-cylinder models of the new E-Class Estate includes rack-and-pinion power steering with a variable ratio. This is more indirect in the central position compared to the predecessor and, therefore, helps to improve handling at high straight-line speeds. However, when the steering wheel angle exceeds around 100 degrees, the ratio becomes more direct, which helps to reduce the number of steering wheel turns required to park or manoeuvre.

The V6 and V8 models are even more responsive thanks to the Direct-Steer system adopted from the SL-Class and available on the four-cylinder models as an optional extra. The variable rack ratio becomes more directly as soon as the angle reaches six degrees. When driving on twisting country roads, i.e. at medium speed and
with medium steering angles, less steering effort is therefore required. The Estate responds more spontaneously and is more manoeuvrable and more agile. This is
particularly noticeable and useful when manoeuvring. At the same time, the speed-sensitive setting of the power steering assistance (parameter setting) requires little steering effort. The indirect arrangement in the central position, on the other hand, ensures excellent straight-line and directional stability when driving at speed on the motorway.

A further highlight is the power steering pump featuring an electrically controlled
solenoid valve which controls a bypass opening and, as a result, allows metering of the oil quantity in line with requirements. This setup reduces the pressure and oil quantity when driving straight ahead – the power steering pump operates with a substantially reduced output and, consequently, helps to save fuel.

As previously, the E-Class Estate is equipped with an individually adjustable steering column with a height adjustment range of +/- 25 millimetres and a reach adjustment range of 60 millimetres – as such, in this respect the Estate significantly exceeds the competition in this market segment. A fully electrically adjustable steering wheel is included if the optional Memory package is ordered.

Rear axle: self-levelling air suspension as standard

In the interests of greater comfort and agility, the multi-link independent suspension so successful for more than 25 years was re-engineered for use in the new E-Class. Modifications included the front cross-bar of the axle housing, which is now supported by the vehicle body over a wider area. This reduces the forces transmitted into the passenger compartment, a comfort feature that is particularly noticeable when crossing transverse joints in the road surface. In keeping with the lightweight-design concept at the heart of the new E-Class series, wheel location components such as struts, hub carriers and the metal sections of the elastomer bearings are largely made of aluminium. The rear-axle subframe is made of high-strength steel.

The E-Class Estate comes with full load-bearing air suspension featuring an automatic self-levelling system as standard. This avoids having to change the spring and rebound travel and helps to ensure comfortable vibration characteristics when fully loaded. In addition, full ground clearance is also ensured at all times.

Air suspension: AIRMATIC with continuously adaptive damping system

All-round air suspension is available as an option for the six-cylinder engine variants of the Estate, and comes as standard on the V8 models. The AIRMATIC air suspension is combined with an electronically controlled damping system that adapts the damper characteristics with continuously variable control and individually for each wheel.

A total of seven sensors monitor the driving situation and the position of the body, sending their information to an electronic control unit, which also processes information concerning road speed, steering wheel angle, braking torque and engine torque, using this data to calculate the optimum shock-absorber characteristics. The system adjusts the damping force for each wheel individually, depending on the current road conditions and driving situation. When driving normally, soft damping settings are also selected if the road surface is poor. This mode offers the E-Class occupants maximum comfort without impairing the outstanding directional stability, road adhesion or handling safety. With a more agile driving style, the damping becomes tauter, thereby meeting the driver's need for a more dynamic ride.

The driver can pre-program the principal vehicle characteristics at the push of a button on the dashboard. There are two modes to choose from: "Comfort" or "Sport". In Sport mode, the hydraulic forces of the shock absorbers are increased so as to allow even better directional stability and road adhesion at high speeds.The stiff suspension configuration is also automatically available in Comfort mode for critical driving conditions.

AVANTGARDE chassis with lowered body

As well as the standard-fit DIRECT CONTROL suspension with steel springs and amplitude-dependent damping system, Mercedes-Benz offers sports-tuned suspension with reinforced anti-roll bars and specially designed 17-inch light-alloy wheels for the AVANTGARDE line. If this suspension system, also available as an optional extra for the other model variants, is specified, the body is lowered by 15 millimetres.
If the AMG Sports packageis ordered, the AVANTGARDE chassis is also equipped with 18-inch wheels, larger brakes and perforated front brake discs.

Brakes: with Hill-Start assist and brake drying function

With the ADAPTIVE BRAKE, the new E-Class offers an innovative braking system
incorporating additional assistance functions for even greater comfort and safety. One example of this is the practical HOLD function: after the E-Class has been braked to a standstill, briefly pressing the brake pedal a little further is all that is required to activate this function. The car is then held by the brakes, even if the driver's foot comes off the brake pedal. In this way, and precisely in the case of vehicles with automatic transmissions, the ADAPTIVE BRAKE prevents the car from rolling forwards when stopped at traffic lights or stuck in stop‑and-go traffic and from rolling backwards when facing up a slope. The HOLD function is deactivated automatically when the car moves off.

If the driver's foot moves abruptly from the accelerator before an emergency stop,
the brake system increases the pressure in the brake lines and brings the pads into contact with the brake discs so that maximum braking power is available as soon as the driver hits the brake pedal. This priming of the brakes allows the system to assist the standard-fit Brake Assist system.

ADAPTIVE BRAKE also has safety benefits in the wet: the system briefly applies the brakes at regular intervals to wipe the film of water from the brake discs and ensure that the brakes are able to perform at their peak. This automatic brake drying function is always activated when the windscreen wipers of the E-Class have been operating for a certain length of time. The finely metered brake pulses are imperceptible to the driver.

Finally, the ADAPTIVE BRAKE assists the driver with hill starts. If the sensors detect that the vehicle is stopped on an uphill slope, a hill-start-assist function is activated automatically, maintaining a constant brake pressure for a brief period. The driver therefore has enough time to move their foot from the brake pedal to the accelerator without the vehicle rolling backwards - particularly convenient in the case of Estates with manual transmissions.

Even more effective brake discs and brake booster

Large front and rear brake discs provide an ideal technical basis for ensuring reliable deceleration in any driving situation. The front and rear discs measure up to 344 millimetres and 320 millimetres in diameter respectively, depending on the engine version.

For brake cooling, the Mercedes engineers have developed two-section aluminium cover plates which have been tested in the wind tunnel. Whilst driving, they direct the cool air from the underbody into the wheel arches and, finally, to the brake discs.

Control systems: electronics for more safety

Anti-lock brakes, acceleration skid control, Brake Assist and the Electronic Stability Program are all of course fitted as standard to all E-Class models. If the vehicle is ordered with a trailer coupling, ESP® vehicle/trailer stabilisation is activated, which detects dangerous oscillating movements of the trailer and re-stabilises it automatically by sending precisely measured brake pulses to the front wheels of the towing vehicle. If the danger is even more acute, the system applies the brakes to reduce the car's speed automatically whilst reducing the engine torque.
As on the previous model, the trailer coupling swivels and has a ball head that does not need to be fitted or removed. It pivots away beneath the body together with its electrical socket, so that it is concealed from sight when not in use. The Estate has a maximum trailer load of up to 2100 kilograms (braked) - a benchmark value for this model class.

The Electronic Stability Program monitors the air pressure in the tyres too, and warns the driver if there is a sudden loss of pressure. To this end, the system continuously compares the rotational wheel speeds, which mainly depend on the vehicle speed, vehicle load and tyre pressures.The control unit also consults other dynamic ESP®sensor readings, such as the lateral acceleration, yaw rate and wheel torque, to help it diagnose tyre pressure loss. The system is therefore able to detect any deviations, and informs the driver accordingly via the central display.
In order to ensure continued mobility in the event of a flat tyre, Mercedes-Benz offers the option of run-flat tyres. These are available in 245/45 R 17 format and feature self-supporting sidewalls, enabling Mercedes customers to continue driving, even after suffering a flat tyre, for up to 50 kilometres at 80 km/h, depending on the vehicle load.

Wheels and tyres: 7.5 J x 16 light-alloy wheels with 225/55 R 16 tyres as standard

The range of wheels and tyres for the new E-Class Estate offers a wealth of personalisation options for the Estate. Mercedes customers have a choice of eleven wheel and tyre combinations in 16, 17 or 18-inch format. All Estate models are fitted as standard with 225/55 R 16 tyres and 7.5 J x 16 light-alloy wheels. The top-of-the-range E 500 model comes with 17-inch light-alloy wheels fitted with 245/45 R 17 tyres as standard.

4MATIC: new all-wheel drive technology saves up to 0.7 litres of fuel per 100 kilometres

For the E-Class Estate, Mercedes-Benz offers a new generation of the 4MATIC all-wheel drive system, which is even more efficient, even lighter and even more compact than the previously installed all-wheel-drive technology. These advantages over the outgoing model are evident in the improved traction and lower fuel consumption.
From the first quarter of 2010, two models will be available with all-wheel drive: the

E 350 4MATIC with a six-cylinder engine developing 200 kW/272 hp consumes 10.2 litres of premium unleaded petrol per 100 kilometres (provisional NEDC combined figure), making it 0.7 litres per 100 kilometres more economical than before. In the case of the E 350 CDI 4MATIC model (170 kW/231 hp), the fuel saving compared to the comparable predecessor model amounts to 0.7 litres per 100 kilometres. The V6 direct-injection diesel engine posts a fuel consumption figure of 7.6 litres per 100 kilometres (provisional NEDC combined figures).

The latest-generation 4MATIC is a Mercedes development that only adds 50 to 70 kilograms of extra weight (depending on model) and boasts a compact design that takes up very little space in the transfer case area. It can therefore be installed without any modifications to the body and without impeding the front-passenger footwell. What's more, the compact design makes for lower noise and vibration levels.
The permanent all-wheel drive system, which works in tandem with the standard-fit Electronic Stability Program (ESP®), really comes into its own in poor weather conditions such as rain, snow or black ice as well as when starting off, accelerating, cornering at speed or driving on poor road surfaces. In these situations, the electronically controlled 4MATIC system greatly enhances traction, directional stability and road adhesion.

These exemplary handling qualities go hand in hand with hallmark Mercedes comfort thanks on the one hand to the selected damper control and on the other hand to the meticulous spring and damper tuning for the all-wheel drive models, which largely replicates that for the rear-wheel-drive models. A further comfort-related aspect of the 4MATIC is the omission of conventional differential locks which, as other all-wheel drive passenger cars show, affect steerability and handling.

Transfer case integrated in 7G-TRONIC automatic transmission

Unlike before, the transfer case is now integrated directly in the 7G-TRONIC transmission. The transfer case consists of a planetary centre differential and two bevel gears, which form the side output to the front axle. The centre differential produces the newly defined torque distribution between the front and rear axles - 45 to 55 percent (previously 40 to 60 percent) - which is noticeable above all in the improved directional stability, road adhesion and traction compared to the outgoing models.

A further highlight of the new powertrain concept is the compact side output to the front axle gear, which is based on a one-stage concept, meaning that a complete gear stage can be omitted compared to the previous 4MATIC drive system. Furthermore, the rear universal joint on the propshaft is integrated in the power take-off output gear. This space-saving design allows the propshaft to the front axle to be routed very close to the transmission without having to make modifications to the bodyshell.
The significantly higher efficiency of the 4MATIC drive system and the resulting lower fuel consumption compared to the predecessor models is largely down to the omission of the gear stage for the transfer case power take-off and an improved oil supply, since the integral design means that the transmission and the transfer case share the same oil circuit.

Multiple-disc clutch with lock between the front and rear axles

The new double-disc clutch located on the centre differential produces a basic locking torque of around 50 Nm between the front and rear axles. In this system, a cup spring preloads the clutch pack with a permanent force. If the wheels on one of the two axles start to spin, the relative movement of the discs causes a friction torque to be transmitted from the faster-turning axle to its slower-turning counterpart.

This principle of variable torque displacement between the front and rear axles
improves the traction, directional stability and road adhesion of the 4MATIC models. The traction assistance provided by the double-disc clutch is especially noticeable when the friction ratio between the tyres and the road is low, since the clutch locks the powertrain mechanically during moderate starting if the friction coefficient between the tyres and the road is less than ” = 0.3 (more or less equivalent to snow). The wheels are prevented from spinning in such a way as to avoid what is known as the "polishing effect", which leads to a reduction in the friction coefficient. Another advantage of the double-disc clutch is the improved load-change characteristics of the 4MATIC models.

Electronic traction system in place of differential locks

4MATIC uses the Electronic Traction System (4ETS), an additional component of the Electronic Stability Program (ESP®), in place of conventional differential locks. It has been modified and now provides an even higher level of comfort and even better traction. 4ETS is activated automatically when one or more wheels lose grip on the road. In this event, 4ETS brakes these wheels automatically and individually, thus increasing the drive torque at the wheels offering sufficient traction at the same time. These millisecond-fast braking pulses achieve nearly the same effect as three differential locks. In addition, the 4ETS automatic braking pulses are based on the speed of the car.

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