The Mercedes-Benz S400 Blue Hybrid

Mercedes-Benz is making waves with its ‘BlueHYBRID’ which has the bodyshell and mechanicals of the S-Class with a modified V6 petrol engine and a compact hybrid module. The German luxury carmaker claims that its S400 BlueHYBRID is the world’s most economical luxury saloon with a spark-ignition engine. In the New European Driving Cycle (NEDC) combined fuel consumption, it is rated at 29.8 miles per gallon, and also has the world’s lowest CO2 emissions in this vehicle and performance class at 190 gms/km.

Mercedes-Benz emphasises that even with such environment-friendly numbers, brisk performance is maintained. The 3.5-litre petrol engine develops 205 kW/279 bhp while the electric motor generates 15 kW/20 bhp with a starting torque of 160 Nm. The combined output is therefore 220 kW/299 bhp with maximum torque of 385 Nm. The S400 BlueHYBRID is also the first production model to use the next generation of batteries with the more efficient lithium-ion process. The battery is specially developed for automotive use and is said to offer more efficient performance.

As mentioned earlier, the model is a S-Class, specifically the S350 and features an extensively modified drivetrain. This encompasses a further development of the 3.5-litre engine, an additional magneto-electric motor, the 7G-TRONIC 7-speed automatic transmission specially configured for the hybrid module, the necessary operating and control electronics, the transformer and a high-voltage lithium-ion battery.

When the brakes are applied, the electric motor acts as a generator and recovers 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 the compact 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.

The centrepiece of the modular, very compact and highly efficient hybrid drive system is the new high-voltage lithium-ion battery. 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 S400 remain unchanged.

Especially on rural journeys and on motorways, the S400 BlueHYBRID is claimed to achieve superior efficiency improvement by moving the so-called ‘operating point’ of the petrol engine to produce a lower specific fuel consumption. The extremely high start-off torque made possible by the boost effect of the electric motor gives the driver a particularly exhilarating feeling of powerful acceleration and yet fuel consumption and emissions are reduced.

The compact electric motor which is installed in the torque converter housing between the engine and speed automatic transmission, improves efficiency even further. This is a 3-phase AC external rotor magneto motor with an operating voltage of 120V. This compact motor also acts as a starter and generator, adopting the functions of both these conventional ancillary units.

The S400 BlueHYBRID has a claimed acceleration time of 7.2 seconds from 0 – 100 km/h and reaches an electronically-governed top speed of 250 km/h. Compared to the conventionally-powered S350, fuel consumption is said to be about 22% better while CO2 emissions are reduced by 21%. To suit the hybrid driver, the well proven 7G-TRONIC automatic transmission has a different control program for the transmission management system. A newly-developed auxiliary oil pump ensures reliable lubrication of the transmission even during phases when the internal combustion engine is switched off. This complex system is managed by the modified high-performance engine control unit. This incorporates extensive functions, and distinguishes between operating conditions such as city traffic, rural journeys, motorway driving or slow manoeuvring.

The driver is also able to monitor the status of the hybrid drive system visually. The instrument cluster has a separate, centrally positioned, display showing the energy flow during boost and recuperation phases, as well as the battery charge status. As is usual at Mercedes-Benz, the development engineers gave safety aspects their very special attention. Knowhow incorporated into the series-production car included long years of Daimler research experience with fuel-cell technology. The challenge lay in not only complying with all the worldwide and inhouse legal crash test requirements, but also in ensuring the greatest possible safety for the electrical components.

Thanks to its compact dimensions and modular design, the additional weight of the overall system is only 75 kgs, including the comprehensive safety systems. The intelligent high-performance 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. Pricing has been mentioned at about a $1500 premium to the S350 and Mercedes says consumers should break even in about 3 years from gas savings.