Mercedes-Benz S 400 BlueHYBRID

By Kevin Miller

09.17.2008

Mercedes-Benz has released information today about its upcoming S 400 BlueHYBRID sedan. Based on a modified S 350 drivetrain, the S 400 BlueHYBRID empolys a combination of a modified V6 gasoline engine and a compact hybrid module, making it the world’s most economical luxury sedan with a gasoline engine. The 3.5-liter V6 develops 279 HP, and the electric motor generates 20 HP with a starting torque of 118 lb-ft. The combined output is 299 HP with a combined maximum torque of 283 lb-ft. The S 400 BlueHYBRID accelerates from zero to 62 MPH in 7.2 seconds, and reaches an electronically governed top speed of 155 MPH.

The European combined fuel consumption rating is 7.9 liters per 100 kilometers (29.7 MPG), compared to the 23.3 MPG combined rating of the standard S 350. It also boasts the world’s lowest CO2 emissions in this vehicle and performance class, emitting just 190 grams per kilometer. The hybrid system adds a reasonable 75 kilograms (165 lbs) to the standard S 350. Mercedes-Benz’s first hybrid will launch in Europe in the summer of 2009, followed by a US launch in September 2009.

The S 400 BlueHYBRID is the first series-production vehicle to be equipped with a lithium-ion battery developed specifically for automotive use. Combined with modifications to the existing V6 engine, the BlueHYBRID system uses a magneto-electric motor, 7G-TRONIC seven-speed automatic transmission specially configured for the hybrid module, high-voltage lithium-ion battery and transformer, plus the necessary operating and control electronics.

The compact hybrid module is a disc-shaped electric motor that also acts as a starter and generator. The electric motor, a 3-phase AC external-rotor magneto motor, has an operating voltage of 120 volts and is installed in the torque converter housing between the engine and the transmission. Dedicated control electronics are used to operate the 3-phase AC electric motor in the 120 V DC network. The current converter is accommodated in the space formerly occupied by the starter. Because the control electronics heat up as a result of electric currents measuring up to 150 amps, the system is equipped with a dedicated cooling circuit.

The hybrid module is used to implement a start/stop function, which switches the engine off when the vehicle is at a standstill and re-starts the engine when when needed for moving off. As in other hybrid systems, the electric motor can boost vehicle acceleration when needed. Mercedes-Benz, then, claims that they system offers a double benefit, as it both helps to save fuel and increases driving enjoyment. Also as in other hybrid systems, when the vehicle is braked the electric motor acts as a generator, and is able to recover braking energy.

The centerpiece of the compact, modular, and efficient hybrid drive system is the new high-voltage lithium-ion battery. The hybrid 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. The lithium-ion battery is installed in the engine compartment, where it replaces the conventional starter battery, so the interior space and luggage capacity of the S 400 remain identical to other S-class sedans.

Advantages over conventional nickel/metal hydride batteries include a higher energy density and better electrical efficiency, as well as more compact dimensions and lower weight. The lithium-ion battery stores energy for the electric motor, and is also connected to the 12 V vehicle electric circuitry via the transformer to supply power to other standard electrical items such as the headlamps and comfort features. The transformer is located in the right front wheel arch, where it facilitates the exchange of energy between the 120 V high-voltage network and the 12-Volt onboard circuits (whose battery is located in the vehicle trunk). This also allows the option of emergency starting with jump leads if the standard battery should lose its charge. To ensure a consistently high level of electrical efficiency, the transformer is also cooled by a dedicated cooling circuit.

The 3.5-liter V6 gasoline engine with variable valve control has been re-engineered for application in the S 400 BlueHYBRID as well. Engineers made use of the 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 7 hp while reducing fuel consumption.

Mercedes-Benz engineers adapted their 7G-TRONIC automatic transmission to suit the hybrid drive, with newly programmed software for the transmission management system. An auxiliary oil pump was added to ensure lubrication of the transmission when the internal combustion engine is switched off. This system is managed by the modified high-performance engine control unit.

To allow the driver to keep track of what the hybrid system is doing, 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.

Perhaps most importantly, the S 400 BlueHYBRID is emblazoned with HYBRID badges visible from nearly every angle. Prominently on display, the badges let other motorists and passers-by know that your S-Class is a hybrid, not just another gas-guzzling luxury sedan. Perhaps next autumn we can expect to see a large number of Priuses traded in to Mercedes-Benz dealers as well-to-do motorists wanting to make a green statement while maintaining their dignity flock to the politically-correct S 400 BlueHYBRID.

COPYRIGHT Autosavant – All Rights Reserved

Author: Kevin Miller

As Autosavant’s resident Swedophile, Kevin has an acute affinity for Saabs, with a mild case of Volvo-itis as well. Aside from covering most Saab-related news for Autosavant, Kevin also reviews cars and covers industry news. His “Great Drive” series, with maps and directions included, is a reader favorite.

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3 Comments

  1. when are they finally going to bring this sort of thing over in a smaller car like the C or A classes?

    economical, my ass!

  2. Interesting that Daimler has basically chosen to use a “mild hybrid” on this rather than the two-mode hybrid that it codeveloped with GM and BMW. I believe that BMW has also abandoned the two-mode system for the most part. The funny thing is that financially, it’s a lot easier for a $70,000 S-class to hide the $10,000 two-mode cost than it is for a $30,000 Tahoe.

  3. Editor – I also find that point interesting. Mild hybrid instead of the two-mode. I’d like to hear why mercedes made that decision.

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