Comfort development for the new C-Class
Mercedes-Benz will launch the new C-Class – a unique syn-thesis of superlative comfort and driving pleasure in this market segment – in spring 2007. This decisive edge comes courtesy of several years of expe-rience, precise Mercedes Codes for comfort and a new development process which the Stuttgart-based manufacturer has implemented for the very first time: digital prototyping. Computer simulations enabled the engineers to define, test and refine the saloon’s major characteristics at a very early stage of development, meaning that even the first ready-to-drive prototypes and pre-production models displayed a high level of maturity. Digital prototyping allowed the Mercedes engineers to make tremendous progress, especially in terms of ride comfort, quiet running, effective climate control and chassis tuning. This process is largely responsible for two of the key characteristics of the new C-Class – driving enjoyment and agility – both of which are of the usual high Mercedes standard.
The new C-Class is the world’s first production vehicle to be designed and developed based on a digital prototype (DPT). In this process, Mercedes-Benz bundles together all of its calculation methods, using around 2130 gigabytes of data to create a completely virtual car. Computer simulation was used to develop and test the crash-safety and occupant-protection systems for the new C-Class as well as the car’s NVH (noise, vibration and harshness), durability, energy management, climate control and aerodynamics. The Sindelfingen engineers use one of the world’s largest IT networks for many of these calculations.
The new DPT process helped to save time and solve trade-offs at an early stage as well as permitting computer testing of the entire saloon concept. This environ-ment created the ideal conditions for the subsequent field-development and road-testing phase, involving 280 real prototypes, which began in the summer of 2003. By the time full production gets underway, the new C-Class will have clocked up a total of over 24 million test kilometres world-wide, making this the largest test programme in the Stuttgart manufacturer’s history.
Computer- and test rig-based test drives with the digital prototype
Comfort and handling were focal points of the development work. The Mercedes experts put the digital prototype through its paces on virtual urban and country roads as well as motorways in order to define the ride comfort at an early stage. This test volume is equivalent to around 2000 individual drives in reality. To tune the handling characteristics, the digital prototype completed more than 1500 computer-based obstacle-avoidance tests, slaloms and braking manoeuvres – many of them in real-time simulations.
In addition the new development process allowed the saloon’s handling character-istics to be experienced subjectively. State-of-the-art test rigs such as the Ride Simulator were programmed with the C-Class data and the road surfaces of real test routes so that the engineers were able to "drive" the new Mercedes model on the test rig very early on in the project. Although the Ride Simulator simulates the saloon’s handling characteristics digitally, it does so realistically.
Over 6000 pages of Mercedes Codes for defining hallmark Mercedes features
Development of the new C-Class was based on a main specifications book containing around 360 pages, This book describes the saloon’s technology right down to the last detail and specifies strict targets – called Mercedes Codes – for important characteristics. Some 150 main criteria, along with thousands of individual targets compiled in 250 component specification books with a total of over 6000 pages, relate solely to the topic of comfort – a key aspect of the C Class alongside safety, reliability, quality and agility.
The Mercedes Codes for comfort reflect the many decades of experience and the vast pool of know-how that the Stuttgart manufacturer has acquired in this area of passenger-car development. As well as defining technical requirements, the Codes take into account scientific analyses performed at DaimlerChrysler’s Customer Research Centre, looking at how motorists perceive comfort subjectively. It was therefore possible to bring technical features into line with sensory perception – a key requirement for ensuring the classic Mercedes driving experience.
Comfort development requires profound and detailed knowledge of how irritating noise and vibration is caused and transferred. Mercedes-Benz analyses a total of around 60 different phenomena in these areas, including the typical lifting, pitching and rolling of the car body as well as many largely unfamiliar phenomena which can mar the comfort experience, such as quivering, micro-quivering, wobble, shimmy, grumble and whine, to name but a few technical terms.
Low-vibration body for outstanding long-distance comfort
The aim of the C-Class development engineers was to combine superlative ride comfort with sporty agility. A quick glance at the saloon’s code book reveals that this goal was achieved: the C-Class easily achieves the stringent Mercedes targets and thus sets the benchmark for long-distance comfort in its market segment. In the case of micro-quivering – the term experts use to describe the comfort characteristics on slightly uneven roads – the readings for the new C-Class undercut the maximum limits specified by Mercedes by as much as 15 percent.
The saloon is equally adept at compensating for the typical body shudder caused by uneven road surfaces, which can be transferred into the interior of the car via the wheel carriers, springs, shock absorbers and mounts. At 140 km/h, the driver of the C-Class feels almost none of this shudder: the figure achieved by the C Class – less than 0.3 m/s² – is around 40 percent lower than the already strict limit imposed in the specifications book.
Key factors which contribute to this high level of ride comfort include an intelligently designed bodyshell which is 13 percent more torsionally stiff than that of the outgoing model, newly developed seats and a standard-fit damping system which adjusts the shock-absorber forces in accordance with the driving style.
Quiet engines and a pleasantly calm interior
Equally impressive progress has been made in the field of acoustic comfort, which the Mercedes engineers have improved by implementing a series of measures, including even more effective acoustic insulation of the interior, sound absorbers in the body cavities and a sophisticated door-sealing concept. The engines and exhaust systems have also been enhanced with respect to comfort. By way of example, a new injection system audibly reduces the combustion noise in the four-cylinder diesel powerplants. The difference can even be heard when the engine is idling. Here the noise level of the four-cylinder CDI engines easily beats the Mercedes target of 62 decibels.
At higher speeds, the body’s excellent aeroacoustics play an important part in ensuring a high level of ride comfort. Wind noise, often perceived as annoying high-frequency hissing in the interior, is practically inaudible when travelling on board the new C-Class.
Based on meticulously calculated empirical values and with the help of the latest development processes, the Mercedes-Benz C-Class opens up a clear lead – taking the concept of superlative comfort and agility to previously unscaled heights.