New Mercedes C-Class: Comfort Development

Press Release

The Mercedes Codes - comfort based on experience

• 360-page specifications book containing Mercedes Codes for comfort

• Targets and know-how the result of years of development work

• C-Class offers highest level of ride comfort in its market segment

• Unique synthesis of technology and emotion

• Innovations in body and chassis technology

Comfort is a multi-facetted topic. It is perceived, experienced and assessed with all the senses. This fact alone highlights the complexity behind the term "comfort". Although objective measured variables can indicate the existence of typical comfort aspects – such as good climate, restful calm, balanced suspension or pleasant feel – none of these variables reflect subjective (i.e. human) perception. And this is what really determines how we experience comfort.

In other words, developing comfort means bringing technical features into line with sensory perception; adapting technology so that it offers people a positive experience in every respect.

Achieving this objective requires one thing above all: knowledge based on experience. In this area of automotive development, Mercedes-Benz has far more experience than any other passenger car manufacturer. Alongside safety, reliability, quality and value retention, Mercedes models have always delivered unsurpassed long-distance comfort.

Based on their many years of research and development work, the Mercedes engineers know how to avoid discomfort and how to achieve comfortableness for car occupants. They also know what appeals to car drivers on an emotional level, how they sense comfort and to what extent they perceive comfort consciously or expect comfort subconsciously. This is where technology and emotion come together. This is where knowledge and experience combine to produce an outstanding result: hallmark Mercedes comfort.

The Mercedes engineers compile their know-how about this and other characteristic features of Mercedes cars in a specifications book – a meticulously acquired and strictly monitored pool of knowledge based on many years of evolution in automotive technology, which gets bigger and, therefore, more valuable, with each passing year and each new model series.

At the start of each development project, the specifications book is rewritten and adapted in line with the model series in question. The book for the new C-Class contains around 360 pages. And 150 of the "Mercedes Codes" defined by targets, measuring instructions and descriptions relate to the topic of comfort alone. They are explained in even more detail in 250 component-specification books comprising a total of around 6000 pages. The aim was to achieve a new dimension in ride comfort in this vehicle category but without neglecting other equally typical Mercedes hallmarks such as safety, agility and quality.

Vibration and noise: from shimmy to grumble

The Mercedes experts describe one of the main aspects of ride comfort with just three letters: NVH stands for noise, vibration and harshness. From the concept phase up until the start of production, NVH was an integral part of every development process. Engineers in various disciplines worked together to create a new comfort experience for the C-Class occupants.

NVH is development work based on experience. In order to achieve hallmark Mercedes comfort, the first job is to pinpoint the type of vibration and noise which can be sensed whilst driving and how this vibration and noise is transferred to the car interior or the ears of the occupants. Hence the Mercedes portfolio of comfort-related vibration and noise comprises around 60 different phenomena, all of which were meticulously analysed, assessed and, if necessary, eliminated whilst the C-Class was being developed.

These audible and perceptible occurrences include the typical lifting, pitching and rolling of the car body as well as many largely unfamiliar phenomena which can be latently present during driving and thus persistently mar the comfort experience: quivering, micro-quivering, wobble, shimmy, grumble and whine, to name but a few NVH terms.

Mercedes-Benz has defined precise targets for each of these 60 or so phenomena in the C-Class specifications book. None of these targets must be exceeded. Viewed as a whole, they essentially form the Mercedes Code for comfort.

A glance at the contents of the Code Book reveals just how much attention the Sindelfingen engineers pay to the topic of comfort and the extent of their achievements with the new C-Class:

• Micro-quivering: this is the term Mercedes experts use to describe the vehicle comfort on slightly uneven roads. The chassis should be capable of largely compensating for this unevenness so that the occupants can enjoy a smooth ride – a prerequisite for excellent long-distance comfort. The new C-Class meets these high Mercedes standards and beats the already impressive target achieved by the outgoing model by around 15 percent.

• Trembling: uneven roads cause the wheels and axles of a car to vibrate (15 to 40 Hertz). These vibrations are transferred to the car body via the wheel carriers, the springs, the shock absorbers and the mounts. The car occupants feel this phenomenon through vibrations on the steering wheel, the seat cushions and the seat backrests. Since continuous trembling movements of this kind mar the driving experience, Mercedes-Benz specifies strict limits for various road speeds. For instance, the steering wheel's rotational acceleration should not exceed 0.5 m/s² at 140 km/h, while the maximum permitted limit on the driver's seat mount is 0.35 m/s². The new C-Class more than meets the requirements of these Mercedes Codes and achieves figures of less than 0.3 and 0.2 m/s² respectively.

Body engineering: torsional stiffness improved by 13 percent

The intelligently designed bodyshell meets important criteria with respect to the excellent ride comfort which distinguishes the new C-Class from other saloons in this market segment. The static torsional stiffness – an important indicator of the body's vibration response – has been improved by around 13 percent compared to the outgoing model. The Sindelfingen engineers paid particular attention to the connecting points between the chassis and body, which have to withstand extremely high loads. They were strengthened in specific areas to prevent the vibrations caused by the road from being transferred to the body so as not to mar the driving experience.

In addition, the stiffness at the points between the powertrain and the body where load is transferred was increased by up to 17 percent - a measure which benefits the saloon's agile handling as well as its vibrational comfort.

When selecting the materials for the body, preference was given to high-strength steel alloys because they minimise weight whilst maximising strength and, therefore, safety. Around 70 percent of all the bodyshell panels for the new C Class are made using these steel grades - a new record in passenger-car development.

Particularly worthy of mention are the sophisticated, ultra-high-strength steel panels that have only been developed in recent years. Their tensile strength is three to four times higher than that of conventional steel grades, thus making them indispensable for meeting the strict Mercedes requirements in terms of durability, safety and vibration response. These high-tech, ultra-high-strength alloys account for around 20 percent of the weight of the new C-Class bodyshell.

New features which are crucial with respect to both occupant safety and body stiffness include the two full-length floor side members which have been further reinforced with additional sections on their insides. At the front end they adjoin the longitudinal members, while at the rear end they reach as far as the cross member below the rear seats and thus stabilise the entire floor structure. This extra stabilisation substantially enhances the body's vibration response.

Chassis technology: damping force adjusted in line with driving style

Newly developed chassis technology provides the ideal foundation for the C-Class saloon's agile and comfort-oriented handling characteristics. Perhaps the most important element is the amplitude-dependent damping system which the C-Class includes as standard. With a normal driving style and low excitation of the shock absorbers, the damping forces are reduced automatically, which has a noticeably positive effect on the saloon's ride comfort without impairing driving safety. However, if the shock-absorber excitation is greater – for example when cornering at speed or when performing evasive manoeuvres – the maximum damping force is applied in order to ensure effective stabilisation of the car.

This technology works by purely hydromechanical means without the need for complex sensors and electronics. It is essentially based on 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 much lower damping force is produced at the shock-absorber valve. The result is "softer" shock-absorber characteristics and, therefore, a high level of ride comfort.

If the excitation of the shock absorber is greater, the control piston moves to its limit position and oil ceases flowing through the bypass duct. As a result, the full damping force is available.

Seats: newly developed foam upholstery with two-zone comfort

The Mercedes engineering team also paid particular attention to the seats, since they can be equally crucial when it comes to long-distance comfort. The result is newly developed front seats which offer further advantages in terms of pressure distribution and lateral support. This was achieved by developing seat contours with more pronounced side bolsters and by using two-zone upholstery: in the outer zones – particularly in the side-bolster areas – the foam is harder so as to provide good lateral support, while the inner zone of the seat surface is softer.

In addition, the foam upholstery used for the seat surfaces is around five percent thicker than in the outgoing model.

In this way, the Mercedes specialists are able to achieve an even pressure distribution and avoid pressure peaks, especially below the ischial-tuber area, which can cause a feeling of unpleasantness on long drives.

The foam upholstery is housed in seat squabs with integral suspension. A frame made partially from high-strength steel forms the solid basis for the front seats. The front seat backrests consist of steel frames and foam elements whose contours, like the seat surfaces, provide even better lateral support. The volume of the foam backrest has been increased by around five percent compared to the seat in the previous C-Class. A standard-fit lumbar support allows the driver to adjust the backrest contours to suit the anatomy of his or her back and so relieve muscle stress – a further factor which enhances long-distance comfort.

Low noise levels: audible progress at idle speed and when driving fast

As well as stringent vibration limits, Mercedes-Benz specifies strict noise limits, again based on several years of experience. These Mercedes Codes take into account all driving situations and conditions – from idling speed to top speed.

• Idling noise and driving noise: this audible comfort-related phenomenon involves the transfer of engine noise to the interior via the engine mounts, integral support frame and body. Mercedes-Benz specifies specific driving-noise and idling-noise limits in the form of Mercedes Codes for every engine variant. At idling speed, the new C-Class easily meets these targets and thus sets new comfort standards in this discipline.

• Hiss: when travelling at high speed, the air flowing around the car body can cause unpleasant, mainly high-frequency wind noise which reaches the interior via the body, the windows, the doors and the sunroof. The Mercedes experts have defined targets which limit the sound pressure level at different frequencies. The sound pressure level in the new C-Class follows this "ideal line" and therefore meets stringent Mercedes requirements regarding acoustic comfort at high speed.

Sound insulation: thicker carpet and specific firewall insulation

The outstandingly low noise levels inside the new C-Class are the result of meticulous work carried out on test rigs and following test drives. The Sindelfingen experts call this work "NVH tuning". And it makes a clearly audible difference. For instance, they developed additional insulation measures which damp vibrations and absorb sound even more effectively than was the case in the outgoing model. One example of this is the carpet in the saloon's interior, whose insulation characteristics have been intelligently enhanced: now the carpet is combined with a foam which is lined on its underside to create a spring/mass system. Not only has the thickness of foam been doubled compared to the outgoing model, the material also covers a larger section of the floor panel and can therefore absorb disturbing noises up to 20 percent more efficiently. The thicker foam, coupled with the foam's excellent insulation characteristics, made it possible to reduce the weight of the heavy layer by up to 50 percent – one of several aspects which contribute to the lightweight design.

The extremely low noise levels are also attributable to the "soundproof" dashboard, whose front section is fully insulated so that no disturbing engine noise reaches the interior, and to the enhanced soundproofing material used for the firewall. The Mercedes engineers used computer simulations to optimise the firewall insulation. Plus they defined the thickness of the sound-absorbing resin foam with pinpoint accuracy, based on the level of noise emmission.

Bodyshell cavities are filled with special foam absorbers which absorb disturbing noise. These elements are first mounted on special support plates and then firmly attached to the body. In the dry zones of the paintshop, the soundproofing materials expand of their own accord and completely fill the cavities. Each of the body's two sidewalls conceals nine of these foam absorbers.

The Mercedes engineers responsible for developing the new C-Class combated the wind noise caused by air flowing around the body and its attachments or by vibration excitation of the panel surfaces by making the bodyshell stiffer using full-length floor side members and reinforced outer skin surfaces. They also employed a new door-sealing concept: the doors of the C-Class now have two or, in crucial areas, even three orbital sealing levels.

Climate comfort: heating and cooling output boosted by up to 15 percent

When it comes to effective climate control, too, the new C-Class outperforms its predecessor by a clear margin. The Sindelfingen engineers have developed two new air conditioning systems. One of them – THERMATIC – is specified as standard for the new saloon. Meanwhile the optionally available THERMOTRONIC system incorporates sophisticated technology which allows three-zone climate control in the car interior – a first in this vehicle category.

Both air conditioning systems have received a boost in heating and cooling output. The heating output has been increased by around ten percent to eleven kilowatts, equivalent to the power of the central heating system in a modern family house. An air conditioning unit whose output is 10 to 15 percent higher than its counterpart in the outgoing model ensures rapid cooling of the interior.

Preventing draughts is a further important aspect of comfort; this is why the Mercedes engineers further enlarged the ventilation outlet opening areas, thus reducing the air flow speed and, therefore, the risk of irritating draughts. A total of 16 outlets effectively and evenly ventilate the interior. With the exception of the defroster outlets below the front windscreen and the outlets in the footwells, all of the ventilation outlets allow infinitely variable adjustment of the air quantity. The THERMOTRONIC system also includes an automatically controlled, upwards-pointing diffuser outlet on the dashboard, which ensures indirect and, therefore, draught-free ventilation.

Sophisticated sensor systems see to it that the ideal temperatures desired by the occupants are kept constant. For instance, two sensors measure the interior temperature and provide the system with even more precise data so that it can react more quickly to temperature fluctuations. The sensors are located in the overhead control panel and next to the electronic ignition lock. In addition, four sensors monitor the temperature of the air flowing out of the ventilation outlets, enabling a continuous comparison between the desired and actual temperatures. A further sensor records the intensity and direction of the sun's rays. These data allow the automatic climate control system to control the air quantity and temperature based on the driving situation or weather conditions, thus making sure that the C Class occupants enjoy a consistently high level of climate comfort.