Mercedes-Benz to market S 400 BlueHYBRID next year

Mercedes-Benz is to bring its first hybrid drive passenger car to market in summer 2009. Based on the S 350, the S 400 BlueHYBRID combines a 205 kW (279 bhp) 3.5-litre V6 petrol engine with a 15 kW (20 bhp) electric motor for a combined output of 220 kW (299 bhp) and a combined maximum torque of 385 newton metres. The new Mercedes will be the world's most economical (7.9 l/100 km) luxury saloon with a spark-ignition engine and will have the world's lowest CO2 emissions in this vehicle and performance class at just 190 grams per kilometre. The motor will use a particularly efficient high-voltage lithium-ion battery specially developed for automotive use and a 7G-TRONIC seven-speed automatic transmission specially configured for the hybrid module.

The compact hybrid module is a disc-shaped electric motor that also acts as a starter and generator. The system offers a double benefit, as it both helps to save fuel and increases driving enjoyment. This is partly due to the booster effect of the electric motor, as it powerfully backs up the petrol engine with a maximum additional torque of 160 newton metres during the high-consumption acceleration phase. The driver benefits from the combined action of these two units in the form of even more impressive torque characteristics and smooth, effortlessly superior acceleration.

The hybrid module also has a comfortable start/stop function, which switches the engine off when the vehicle is at a standstill – for example at traffic lights. When it's time to move off again, the electric motor almost imperceptibly restarts the main power unit. This likewise makes a contribution to fuel economy and environmental protection: because the engine restarts first time, and practically instantly, emissions are also minimised during the starting phase.

When the vehicle is braked the electric motor acts as a generator, and is able to recover braking energy by a process known as recuperation. Working in finely tuned partnership, the electric motor supplements the braking effect of the petrol engine and the wheel brakes to deliver a smoothly progressive braking action. The recuperated energy is stored in a compact yet highly efficient lithium-ion battery in the engine compartment, and made available when required. This complex system is managed by a high-performance control unit, which is likewise located in the engine compartment.

A milestone on the road to electrification

The centrepiece of the modular, very compact and highly efficient hybrid drive system is the new high-voltage lithium-ion battery, which was specially developed for automotive use and is the first such unit worldwide to be introduced in a series-production vehicle. In this way Mercedes-Benz is making a trailblazing contribution to the electrification of the car, with the S-Class once again playing the role of the technological trendsetter.

Major advantages over conventional nickel/metal hydride batteries include a higher energy density and better electrical efficiency, together with more compact dimensions and a lower weight. Thanks to space-saving installation in the engine compartment, where it replaces the conventional starter battery, the generous interior space and boot capacity of the S 400 remain unchanged. The lithium-ion battery not only stores energy for the electric motor, but is also connected to the 12-Volt onboard network via the transformer to supply power to other standard consumers such as the headlamps and comfort features. The completely newly designed battery system consists of the cell block with its lithium-ion cells and the cell monitoring system, the battery management function, the high-strength housing, the cooling gel, the cooling plate, the coolant feed and the high-voltage connector.

Optimised thermal efficiency lowers the engine's fuel consumption

The 3.5-litre V6 petrol engine with variable valve control has been throughly re-engineered and improved. In the process the development engineers made use of the advantages offered by the Atkinson principle,where the expansion phase is longer than the compression phase. The intake valve is kept open slightly longer between the intake and compression phases, which improves the engine's thermal efficiency while reducing the specific fuel consumption and untreated emissions. A new cylinder head, different pistons and a modified camshaft with different camshaft control increase the output by 5 kW/7 hp to 205 kW/279 hp – while reducing fuel consumption at the same time.

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