All the engines for the C-Class are now classed as BlueEFFICIENCY units, showing that they are particularly efficient and environmentally compatible in their use of fuel. A reduction of up to 31 percent has been achieved in fuel consumption.

All the C-Class models are equipped with the ECO start/stop function as standard from market launch (with the exception of the C 300 CDI 4MATIC). In future all automatic versions with the exception of the C 300 CDI 4MATIC will feature the further-developed 7G-TRONIC PLUS seven-speed automatic transmission (introduction in the C 250 CDI 4MATIC in June 2011). In addition, the overall ratio of all new powertrain variants has been optimised for fuel economy.

All the petrol engines in the model series have direct injection. One of the highlights is the introduction of the new V6 petrol engine with its innovative and highly efficient BlueDIRECT process in the C 350 BlueEFFICIENCY. The quantum leap in efficiency is particularly well illustrated by the six-cylinder unit: power has increased considerably, the C 350 BlueEFFICIENCY delivering 225 kW (306 hp) and 370 Nm (C 350 previously 200 kW (272 hp) and 350 Nm). Fuel consumption has been significantly reduced, however: the C 350 BlueEFFICIENCY has a mean consumption of 6.8 litres per 100 km – 3.1 litres or 31 percent less than the preceding C 3503 model. When compared with the previous direct-injection engine, too, the 350 CGI, the new C 350 BlueDIRECT achieves a consumption saving of 18 percent.

3 Figures for the saloon
The four-cylinder petrol engines, which made a great evolutionary leap forward in 2009 and all feature direct injection and turbocharging, excel with high performance and exemplary economy. Known internally as M 271 EVO, the four-cylinder petrol engine model series stands for systematic downsizing. The direct fuel injection facilitates higher compression and thus a better thermodynamic efficiency rate, which becomes apparent where fuel consumption is concerned: the new four-cylinder direct-injection engines also consume up to 31 percent less fuel than the comparable V6 engines of the preceding model.

With a range of new features, the new four-cylinder petrol engine is completely different to its predecessor. The core element of the new engine is the homogeneous direct injection. At a pressure of up to 140 bar the fuel is fed via a high-pressure line to injectors leading to the combustion chamber. This lowers fuel consumption and also considerably reduces pollutant emissions. In addition to this, a variable oil pump has been developed, as has a heat-management process which stops the coolant circulation when the engine is cold, so that the engine and engine oil heat up faster during a cold start. What’s more, the camshaft adjusters have been further optimised as vane-type adjusters, and using an integral control valve they facilitate rapid, continuously variable adjustment of the most favourable timing – and therefore a high torque even at low engine speeds. The crankshaft is manufactured from die-cast aluminium, whilst the cylinder head is made of a special high-strength aluminium alloy.

C-Class petrol models at a glance

The diesel engines: yet again much more frugal
The most economical model in the Mercedes C-Class has also become even more frugal: the C 220 CDI BlueEFFICIENCY with the manual six-speed transmission and the standard ECO start/stop function has a mean diesel consumption of 4.4 litres per 100 km – 0.4 litres less than before. This corresponds to 117 grams of CO2 per kilometre. In conjunction with the improved 7G-TRONIC PLUS automatic transmission and the ECO start/stop function included as standard, the C 220 CDI BlueEFFICIENCY and C 250 CDI BlueEFFICIENCY both deliver top-class figures with a combined diesel consumption of just 4.8 litres per 100 km. This corresponds to CO2 emissions of 125 grams per kilometre.

C-Class diesel models at a glance

Seven gears: the 7G-TRONIC PLUS automatic transmission now in the C-Class
More is more. Whilst many C-Class models have up until now enjoyed convenient automatic gear-shift operation courtesy of a five-gear automatic transmission, with immediate effect seven gears will always be available. This means that the automatic transmission will be able to react even more sensitively to the driver’s wishes: at full acceleration even more torque will be available, whilst the engine speed is lowered for more economy during relaxed cruising. And because of the reduction in jumps where the engine speed is concerned, the gear changes become even more imperceptible and comfortable.

The C-Class has been given the latest evolution level of the 7G-TRONIC automatic transmission with the suffix “PLUS” – it features enhanced fuel consumption and comfort. The new generation of the torque converter provides an improved dynamic response, better durability and reduced noise and vibration levels thanks to a new hydraulic circuit, as well as enhanced dampers and torque converter housing.

The extreme wheel-slip reduction of the torque converter housing, combined with larger mechanical damper de-coupling, helps to reduce consumption significantly. In addition, the gearshift program in ECO mode has been changed in favour of lower engine rpm at cruising speeds. With friction-optimised bearings and seals plus a new automatic transmission oil (FE-ATF) with reduced viscosity in conjunction with an optimised additive package, the transmission itself helps to cut consumption. The higher longevity of the new transmission oil results in new oil-change intervals (every 125,000 kilometres) if the cooling thresholds are adhered to.

The transmission’s improved electrohydraulic unit and the new friction-reducing materials on some transmission parts in conjunction with optimised software result in better shift quality. And via an electrically driven oil pump the 7G-TRONIC PLUS keeps the transmission on standby during stops – an important prerequisite for fast, comfortable starts in conjunction with the ECO start/stop function.

Start/stop function: sophisticated technology gives the highest levels of efficiency
When the car is at a standstill, the engine does not need to be running and therefore does not need to consume fuel. Recognition of this essentially simple fact is behind the ECO start/stop function, which is now available in the C-Class with the 7G-TRONIC PLUS automatic transmission. In order to implement the auto start and auto stop function with a very high level of comfort in a Mercedes-Benz, it has been necessary to develop complex control logistics and a series of new or modified components, such as a high-output starter motor. That’s because Mercedes drivers should only really notice the forced breaks taken by the engine when they are at the filling station.

As a general principle, the engine is switched off every time the vehicle comes to a standstill (auto-stop function). Restarting the engine (auto-starting function) takes place almost imperceptibly; and moving off without any noticeable time lag compared to a stationary vehicle with its engine running. This rapid action is attributable to a special feature: an additional electric transmission oil pump supplies the clutches of the automatic transmission with oil pressure in the stop phases, so as to enable a swift resumption of the journey after direct starting of the combustion engine via the ECO start/stop function. The starter has also undergone thorough modification: it is now designed to cope with eight times as many starting procedures as a conventional starter, ensuring that it will last a car’s lifetime in continuous urban driving involving frequent auto-starting.

It is not always expedient for the engine to be shut down automatically when the vehicle comes to a standstill. The auto-stop function will therefore only be initiated if a number of conditions are met. Where the vehicle itself is concerned these include a certain coolant temperature being reached or the availability of sufficient voltage in the on-board electrical system. The system also checks whether the doors and the bonnet are closed, and whether the driver’s seat belt buckle is fastened. This prevents unintended starting of the engine, for instance when the engine oil is being checked.

Auto-starting takes place when the engine is in auto-stop mode, so when the engine has been shut down via the engine-stop function and the ignition remains switched on. One of the following conditions must also be met, for example: the accelerator is depressed, a gear is engaged or the vehicle is in motion.

Thinking cap on: children playing in the vehicle are protected
But the start/stop function thinks one step further still: the forced engine start is also available as a convenience and protective function, whereby the engine is started autonomously via the engine control unit without intervention from the driver. This happens if one of the above-mentioned in-vehicle boundary conditions for the auto-stop function are no longer met, such as the on-board electrical system’s voltage or the desired interior temperature. The engine is also force-started if the driver removes their seat belt or opens the driver’s door. The driver is then forced to actively turn off the engine before getting out of the vehicle, thus safely deactivating the ECO start/stop function when the vehicle is parked. This prevents the vehicle from being started unintentionally, by children playing in it, for instance.

Source: Daimler AG