2008-09-22 - Mercedes-Benz is launching its first passenger car model equipped with a hybrid drive system in summer 2009: the S400 Blue Hybrid. The new model is based on the S350 and features a modified drivetrain. This encompasses a further development of the 3.5 litre V6 petrol engine, an additional magneto-electric motor, the 7G-Tronic seven-speed automatic transmission specially configured for the hybrid module, the necessary operating and control electronics, the transformer and a high-voltage lithium-ion battery. Thanks to its compact dimensions and modular design, the additional weight of the overall system is only 75 kilograms - including the comprehensive safety systems.

The combination of a modified V6 petrol engine and a compact hybrid module makes the model one of the most economical luxury saloons with a spark-ignition engine. According to the German car manufacturer the New European Driving Cycle combined fuel consumption is a mere 7.9 litres per 100 kilometres resulting in the lowest CO2 emissions in this vehicle class of 190 grams per kilometre. The 3.5 litre petrol engine develops an output of 205 kilowatts; the electric motor generates 15 kW and a starting torque of 160 Newton metres. The result is a combined output of 220 kW and a combined maximum torque of 385 Newton metres. The compact hybrid module is a disc-shaped electric motor that also acts as a starter and generator. The system offers both fuel consumption and performance. 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 hybrid module also has an electronic Start/Stop function, which switches the engine off when the vehicle is at a standstill. When it is time to move off again, the electric motor restarts the main power unit. 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.

The centrepiece of the modular hybrid drive system is the new high-voltage lithium-ion battery, which was specially developed for automotive use. 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. 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 engine management system responds very sensitively to different driving conditions, and optimally configures the drive system for the relevant application, ensuring that both fuel consumption and emissions are kept to the lowest possible level. Dedicated control electronics are required to operate the three-phase Alternating Current electric motor in the 120-Volt high-voltage Direct Current network. The current converter is accommodated in the space formerly occupied by the starter. As the control electronics heat up as a result of electric currents measuring up to 150 ampere, the system is equipped with its own, additional low-temperature cooling circuit.

Daimler’s S400 BlueHybrid, due out in mid-2009, is slated to become the first hybrid car with an electric motor powered by a lithium-ion battery.

At 26kg and the size of a briefcase – compared with Toyota’s and Honda’s more cumbersome nickel-hydride batteries, which take up a large portion of their vehicles’ boot space – Mercedes hopes its battery, and its luxury S-Class, can wrest some control from Japanese automakers who have dominated the electric car market until now.

The new hybrid represents a world record in fuel economy for luxury cars, according to Mercedes. By combining a fuel motor with an electric motor, which stores brake energy released on acceleration, the dual engine – a 279-horsepower V6 supported by a 20-horsepower electric motor – enables a top speed of 155mph and 0-60mph acceleration in 7.2 seconds.

Yet it consumes just 7.9 litres of petrol per 60 miles (30 miles per gallon) compared with the conventional Mercedes S350, which consumes 10.1 litres (23mpg).

“The lithium-ion battery is the key component for [making vehicles] electric and for creating sustainable mobility,” said Eva Wiese, spokesman for technologies and environmental communications at Mercedes-Benz in Stuttgart. The new technology applies not only to hybrid vehicles, she said, but to all battery-operated vehicles, including plug-in hybrids, full hybrids and electric vehicles.

Mercedes’ green gamble doesn’t stop there. The company will roll out a series of all-electric Smart cars next year (a test fleet of 100 is currently plying the streets of London), with plans to produce an electric version of its

A-Class by 2010 – both powered by lithium-ion batteries.

However, the 120-volt battery won’t be cheap – at least not at first. With cells produced by a French supplier, Saft, initial cost estimate for the lithium-ion battery are €1,500 (£1,200).

Karl-Thomas Neumann, the CEO of Continental, which developed the battery, called the technology an “important breakthrough” that will help fuel 2m new hybrid cars reaching the market by 2012, which will drastically lower costs.

Mercedes, which lagged for many years developing its place in the hybrid market, faces stiff competition. Peugeot and Citroën are pushing their hybrid and electric technologies at the Paris Auto Show in October, while Renault, Mitsubishi and General Motors have staked out ways to go electric.

Only its fellow German automaker, Volkswagen, which unveiled its latest Golf model two weeks ago – with neither hybrid nor electric options – has been slower warming to the hybrid future.