The 2010 Mercedes-Benz E-Class: Chassis and Suspension
The shock absorber system in the 2010 E-Class works by hydromechanical means without the need for sensors or electronics
by Thomas Philips | 11 March 2009
The newly developed DIRECT CONTROL suspension with standard-fit amplitude-dependent damping system is one of the major factors behind the high degree of long-distance comfort provided by the E-Class. The shock absorbers adapt to the current driving situation, reducing the damping forces automatically when driving normally with low shock-absorber impulses and increasing the forces up to the maximum as required when cornering at speed or performing evasive manoeuvres. In this way, the chassis and suspension meet driver requirements in terms of road roar, tyre vibration and agility – without ever compromising on active safety.
The shock absorber system works by purely hydromechanical means without the need for sensors or electronics. Its core components are a bypass duct in the shock absorber’s piston pin and a control piston which moves in a separate oil chamber. When the shock-absorber bounce is low, the control piston moves oil through the bypass duct so that a lower damping force is produced at the actual shock-absorber valve. The result is “softer” shock-absorber characteristics and, consequently, 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.
Mercedes-Benz has modified several aspects of the three-link front suspension with McPherson struts and, as a result, has achieved excellent results in terms of ride comfort. In the interests of optimal axle kinematics, more favourable vibration characteristics and enhanced safety, the lower link level consists of two individual elements that serve as torque and cross struts. As well as offering more precise wheel location, the main benefit of these struts is that they allow better compensation for vibrations caused by tyre imbalance and fluctuations in braking forces than rigid wishbones. In addition, more crumple space is available in the event of a frontal crash. The third front-axle link is the track rod which connects the transversely installed steering gear to the wheels.
The spring struts consist of cylindrical, transverse force-compensating coil springs, double-tube shock absorbers and newly developed three-phase head bearings. In order to further optimise ride comfort, the Mercedes experts have chosen a starkly upright position for the spring strut so as to reduce the forces acting on the torque strut bearing. As a consequence, it was possible to reduce the bearing rigidity, 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 front anti-roll bar is connected to the spring strut, which is likewise actively involved in locating the front wheels.
Intelligent use of aluminium and steel reduces the weight of the front axle by twelve percent compared to the outgoing 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 at specific points (see page 56). 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
As well as modifying the chassis and suspension, the Mercedes experts have newly developed the steering for the new E-Class, thus further enhancing steering precision, response and steering comfort. Standard equipment for the new E‑Class includes rack-and-pinion power steering with a variable ratio, which is more indirect in the central position compared to the outgoing model and, therefore, helps to improve directional stability and road adhesion at high speed. When the steering wheel angle exceeds around 100 degrees, the ratio becomes more direct to reduce the number of steering wheel turns required to park or manoeuvre.
Mercedes-Benz offers the Direct-Steer system that has proven such a resounding success in the SL-Class as an optional extra (standard for the V6 and V8 models). It fully lives up to its name by providing the driver with more direct response when cornering and, therefore, even more agile handling. In short, it delivers even more driving enjoyment. Hence the Direct-Steer system offers all the benefits of the previously installed speed-sensitive power steering system – less steering effort is required at low speed, when manoeuvring or parking, for example – whilst also enhancing handling dynamics.
The variable rack ratio, which adjusts in line with the steering angle, increases sharply as soon as the angle reaches five degrees, meaning that the driver does not have to move the steering wheel a great deal when cornering. The E-Class responds more spontaneously, and the driver has even more control over the car when greater manoeuvrability and agility are required, such as when driving on twisting country roads, i.e. at medium speed and with medium steering angles.
In other driving situations, meanwhile, the system offers the same advantages as the proven speed-sensitive power steering system and even goes one step further in some cases. For instance, the new Mercedes steering can be even more indirectly configured in the central position than previous steering systems, giving the driver an exceptionally assured steering feel when driving at high speed as well as improving straight-ahead driving and directional stability. When driving slowly or parking, the new technology combines with the speed-sensitive power steering to provide even more comfort than before because the direct ratio further reduces the steering effort required.
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 is equipped with an individually adjustable steering column with a height adjustment range of +/- 25 millimetres and a reach adjustment range of 25 millimetres – meaning that, in this regard, the new E‑Class offers far more adjustability than other saloons in this market segment. A fully electrically adjustable steering wheel is included if the optional Memory package is ordered. To greatly enhance occupant safety, the steering column has been designed to collapse telescopically when hit by the driver with a certain degree of force in the event of a frontal collision. The extended deformation path, which is up to 100 millimetres longer, reduces the forces exerted on the driver’s upper body if a collision occurs.
Rear axle: multi-link independent suspension modified in several key areas
Mercedes’ multi-link independent suspension, which has proven itself time and again over a period spanning more than 25 years, has been further modified for use in the new E-Class in order to meet more stringent requirements in terms of comfort and agility. Modifications include the axle carrier’s front cross-bar, which now has a larger support base at the connecting points with the car’s body. As a consequence, the forces that can be transferred into the passenger cell are reduced: a comfort benefit that is particularly noticeable when driving over expansion joints running across the road, for example.
In keeping with the lightweight-design concept at the heart of the new E-Class, 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.
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 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 package is ordered, the AVANTGARDE chassis is also equipped with 18-inch wheels, larger brakes and perforated front brake discs.
Air suspension: available in combination with continuously adaptive damping system for the first time
The new E-Class is the first Mercedes-Benz model to feature a combination of AIRMATIC air suspension and an electronically controlled damping system that adapts the damper characteristics with continuously variable control – individually for each wheel. This air suspension setup is available as an option for the V6‑powered E 350 CGI BlueEFFICIENCY and E 350 CDI BlueEFFICIENCY models and for the E 350 CDI BlueEFFICIENCY 4MATIC and E 350 4MATIC models; it is fitted as standard for the E 500/E 500 4MATIC models.
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. As the driving style becomes more dynamic, the shock-absorber settings are adapted continuously and therefore meet the driver’s need for enhanced agility.
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 as well as reduce understeer at speeds of up to 120 km/h.
Newly developed McPherson struts
The Mercedes engineers have newly developed or modified many key aspects of the air suspension system. One particular highlight is the wheel-locating McPherson air suspension strut on the front axle, which combines the shock absorber, air bellows and air reservoir. The air bellows is much larger than on the outgoing model and has been further optimised using a new material. The special shape of the air bellows made it possible to use a McPherson air suspension strut in a luxury saloon for the first time.
Likewise, the experts paid special attention to the head bearings for the new air suspension struts, which have to transfer all the forces and, therefore, need to be capable of withstanding extremely high loads in both the compression and rebound stages. These requirements are fulfilled by an extremely rigid, diecast-aluminium flange that supports the bearing. It is the result of painstaking computer simulations and calculations of the complex interplay between the spring strut and the body. Its special design ensures ten times greater stiffness at the point where forces are applied in the air suspension strut area compared to the outgoing model. As a consequence, the newly developed spring strut bearings are one of the main reasons behind the exemplary vibration characteristics at the front of the car. Incidentally, the same benefits are achieved even if steel suspension is fitted.
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, 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 to the brake pedal 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.
The ADAPTIVE BRAKE enhances safety in the wet by sending brief braking pulses at regular intervals to remove the film of moisture from the brake discs, allowing the brakes to work to full effect. This automatic brake drying function is always activated when the windscreen wipers on the E-Class have been operating for a certain time; the driver never even notices these precisely metered brake pulses.
Finally, the ADAPTIVE BRAKE assists the driver with hill starts. If the sensors detect that the Saloon is stopped on an uphill slope, a hill-start-assist function is activated automatically, maintaining a constant brake pressure for a brief period to prevent the E-Class from rolling backwards. The driver therefore has enough time to move their foot from the brake pedal to the accelerator without having to use the foot-operated parking brake.
Even more effective brake discs and brake booster
Large front and rear brake discsprovide an ideal technical basis for ensuring safe and 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 and ensure that, whilst driving, the cool air flows from the underbody into the wheel arches and, ultimately, to the brake discs.
Further technical highlights in the new E-Class include the pedals. For the first time, Mercedes-Benz has used a steel and plastic hybrid design for the pedal support, which reduces weight and takes up less space than the previously used technology. The brake pedal, made from two shells that are welded together, is attached in this support. The shell design likewise helps to reduce weight and also ensures high torsional stiffness and bending strength.
Control systems: electronics for safe motorin
When it comes to active safety systems too, the E-Class features an array of state-of-the-art technology as standard, including anti-lock brakes, acceleration skid control, Brake Assist and the Electronic Stability Program. For ESP®, Mercedes‑Benz has developed control logicthat offers the driver even more effective assistance in critical cornering situations: precisely measured brake pulses sent to up to three wheels cause a moderate reduction in the car’s speed and help it to turn into the bend.
ESP® vehicle/trailer stabilisation, which is activated if the E-Class is equipped with a trailer coupling, detects dangerous oscillating movements of the trailer and restabilises 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 as well as reducing the engine torque before the precisely measured brake pulses are sent to the wheels to stabilise the trailer.
As an option, Mercedes-Benz can equip the new E-Class with a swivelling trailer coupling featuring a ball head that does not need to be fitted and removed every time it is used. Together with the socket, it swivels forwards underneath the body and cannot be seen when not in use. The E-Class has a maximum towing capacity of up to 2100 kilograms (braked) – a new record in this vehicle category.
The Electronic Stability Program also monitors the tyre inflation pressure and, if one of the tyres loses pressure suddenly, warns the driver. To do this, the system continuously compares the wheel speeds, which are dependent on the road speed, the vehicle load and the tyre inflation pressure. In addition, the control unit also analyses other dynamic handling-related ESP®sensor signals such as lateral acceleration, yaw rate and wheel torques in order to diagnose pressure loss in a tyre. Hence the system can detect discrepancies and indicate the information on a central display for the driver.
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 for up to 50 kilometres at 80 km/h, depending on the vehicle load.
Wheels and tyres: 16-inch light-alloy wheels as standard
The range of wheels and tyres for the new E-Class offers a wealth of personalisation options for the Saloon. Mercedes customers have a choice of twelve wheel and tyre combinations in 16-, 17- or 18-inch format. The four-cylinder E 200 CDIBlueEFFICIENCY, E 220 CDIBlueEFFICIENCY and E 200 CGIBlueEFFICIENCY models are equipped with 16-inch nine-spoke light-alloy wheels and low-rolling-resistance 205/60 R 16 tyres as standard. Thanks to a special forging technique, the weight of the wheels has been reduced by a total of 9.6 kilograms.
For the E 250 CDI, E 350 CDI, E 350 BlueTEC, E 250 CGIand E 350 CGI BlueEFFICIENCY models, Mercedes fits 225/55 R 16 tyres and 7.5 J x 16 light-alloy wheels as standard. The top-of-the-range E 500 model is shod with 18-inch light-alloy wheels and 245/45 R 17 tyres ex factory.
For the ELEGANCE and AVANTGARDE lines, and for the AMGSports package, the Mercedes designers have selected special wheels and tyre sizes as standard equipment:
ten-twin-spoke light-alloy wheels in
7.5 J x 16 format, tyre size 225/55 R 16
five-twin-spoke light-alloy wheels in
8 J x 17 format, tyre size 245/45 R 17
AMG Sports package:
five-twin-spoke light-alloy wheels
front: 8.5 J x 18 format with 245/40 R 18 tyres
rear: 9 J x 18 format with 265/35 R 18 tyres