From spring 2008, Mercedes-Benz will be adding three extra-economical BlueEFFICIENCY saloons to the C-Class range. A raft of intelligent measures and technologies has enabled the fuel consumption of the high-volume C 180 KOMPRESSOR and C 200 CDI models to be reduced by up to twelve per cent, while retaining the high levels of comfort and safety typical of a Mercedes. The BlueEFFICIENCY version of the 100 kW/136 hp C 200 CDI consumes only 5.1 litres per 100 kilometres, while the C 180 KOMPRESSOR BlueEFFICIENCY with 115 kW/156 hp covers 100 kilometres with 6.5 litres of premium petrol. This corresponds to 135 and 156 grams of carbon dioxide, respectively, per kilometre. The third BlueEFFICIENCY C-Class model on show in Geneva is the C 350 CGI with direct petrol injection. The six-cylinder unit burns around ten per cent less fuel than the saloon with the current V6 engine.
For the new BlueEFFICIENCY models, Mercedes engineers have harnessed potentials from all fields of development to reduce weight, aerodynamic drag and rolling resistance yet further, and to organise the onboard energy management of these saloons even more efficiently. Together, these measures add up to a fuel saving on the NEDC driving cycle of 0.9 litres per 100 kilometres for the C 180 KOMPRESSOR, and 0.6 litres for the C 200 CDI.
The specialists in Sindelfingen have made very detailed improvements to the comprehensive lightweight construction concept of the C-Class, and have managed to shave off between 19 and 32 kilograms of weight depending on the model. This achievement is in part due to a newly developed windscreen made of laminated glass, which weighs around 1.2 kilograms less than before. This is made possible by a technology transfer from the Maybach luxury saloon: between the panes of glass lies a new, acoustically effective plastic membrane which efficiently absorbs wind noise. This has enabled Mercedes engineers to reduce the thickness of the windscreen, achieving a further weight reduction without compromising noise comfort in any way.
The noise-insulating lining of the firewall has also been weight-optimised with the help of special materials and the latest calculation methods. Using computer simulations, Mercedes-Benz recalculated the required firewall insulation and precisely redefined the material thickness of the sound-absorbing resinous foam in line with the noise input. This needs-driven redesign reduces the weight of the lining by around 20 per cent.
Forged lightweight wheels also have a positive effect on the weight. These tip the scales at around 1.8 kilograms less than conventional light-alloy wheels, saving a total of more than seven kilograms per vehicle. These new lightweight wheels (6 J x 16 ET 39), which have aerodynamic benefits too, are standard equipment for the new BlueEFFICIENCY variants of the C 180 KOMPRESSOR and C 200 CDI.
Newly developed tyres: 17 per cent less rolling resistance
In addition to lightweight construction measures, Mercedes-Benz also devoted particular attention to reducing rolling resistance and aerodynamic drag. In collaboration with Michelin, Mercedes engineers developed lightweight tyres with a particularly low rolling resistance. These are now receiving their series production premiere in the C-Class, and help to reduce fuel consumption.
Rolling resistance is primarily caused by tyre deformation as the tyre contacts
the road surface. This has a braking effect on the car, since additional energy is required to overcome this deformation resistance - therefore, the higher the rolling resistance, the higher the fuel consumption. Up to around 100 km/h, rolling resistance has a greater effect on fuel consumption than aerodynamic drag.
The belt of this newly developed tyre for the C-Class contains a multi-layered mesh of high-strength steel for less deformation. It is also lighter in weight than conventional designs, enabling a further 1.7 kilograms or so to be saved per set of tyres. The secret, however, mainly lies in the chemical composition: the rubber compound for the treads and side walls is designed to ensure that rolling resistance is reduced by 17 per cent, while retaining the same good handling and braking characteristics.
Aerodynamic fine-tuning: Cd figure an outstanding 0.25
At 120 km/h, the aerodynamic drag of the vehicle body already accounts for around 50 per cent of all the dynamic resistance a passenger car must overcome. Accordingly Mercedes-Benz has been very active in the field of aerodynamics for many years, and has achieved remarkable advances that have had a positive impact on the fuel consumption figures of cars bearing the Mercedes star.
With a drag coefficient (Cd figure) of 0.27, the C-Class is among the most aerodynamically efficient notchback saloons in its market segment. This is the result of a whole series of intelligent details, such as the tail lights with ventilation slits: these reduce drag by influencing the airflow along the side walls, causing it to break off at the tail lights without causing turbulences behind the vehicle's rear end. In this way the patented tail lights of the C-Class replace the usual spoiler lips.
In the new BlueEFFICIENCY versions of the C 180 KOMPRESSOR and C 200 CDI, Mercedes engineers have succeeded in bettering even the highly impressive Cd figure of the C-Class with a number of other detailed measures:
Smooth underbody cladding ensures that the air can flow beneath the vehicle body without turbulences. The full engine compartment and underbody panelling of the diesel models is also standard equipment in the BlueEFFICIENCY version of the C 180 KOMPRESSOR.
-Partially blanking off the radiator grille reduces the airflow into the engine compartment, thereby lowering wind resistance. Adequate cooling of the four-cylinder engines is of course uncompromised by this measure.
-Sealing the joins between the bonnet and headlamps, as well as between the bumper and headlamps, improves the airflow around the front end.
-The housings of the exterior mirrors were developed in the wind tunnel, and are particularly streamlined in form.
-Lowering the suspension by 15 millimetres reduces aerodynamic drag, and has a particularly noticeable effect at higher speeds.
-The design of the new lightweight wheels also meets aerodynamic requirements, and improves the airflow around the vehicle flanks.
Thanks to this package of aerodynamic measures the Cd figure for the new BlueEFFICIENCY models has been reduced by seven per cent to 0.25, representing another major contribution to fuel economy.
Efficient energy management: needs-driven power steering control
It is not only intelligent lightweight construction, tyres with a low rolling resistance and good aerodynamics that help to further improve the economy and environmental compatibility of today's passenger cars. Intelligent control of ancillary units and the reduction of friction losses can also make an important contribution in this respect.
Energy management is the key: in the BlueEFFICIENCY models of the C-Class, the power steering system is controlled on a needs-driven and therefore energy-saving basis. The standard power steering in the C-Class has an additional valve which switches off the servo pump when it is not required. While this pump operates continuously in all driving situations in conventional steering systems, the new valve interrupts the flow of hydraulic fluid when the car has followed a straight course for a while, switching off the servo pump. This has the advantage that the engine no longer needs to provide energy to drive the servo pump, meaning that it operates more economically. Thanks to this technology, the NEDC fuel consumption is cut by 0.14 litres per 100 kilometres - which equates to a reduction of 2.5 per cent in the case of the C 200 CDI.
As a further contribution to reduced weight and friction, the BlueEFFICIENCY C 180 KOMPRESSOR and C 200 CDI saloons are equipped with a newly developed final drive featuring further-improved antifriction bearings, forged differential gears and a sophisticated lightweight construction. These measures reduce the friction forces within the transmission, hence the engine expends less energy in overcoming them.
The longer final-drive ratios of the BlueEFFICIENCY versions also help to reduce fuel consumption. These are as follows:
C 180 KOMPRESSOR: 2.87 : 1 (rather than 3.07 : 1)
C 200 CDI: 2.47 : 1 (rather than 2.65 : 1)