2010 Lexus LS600hL and 2010 Mercedes-Benz S400 Blue Hybrid

Don Sherman
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The sumo wrestlers of the auto world, Lexus and Mercedes-Benz, flex their engineering muscles and flaunt their advanced technology every chance they get. Each wages battle in the hybrid luxury sedan category in a distinctive manner.

The Lexus LS600hL's hybrid powertrain accentuates performance and sophistication, not fuel efficiency. A 5.0-liter V-8 collaborates with two electric motor-generators, two planetary gear sets, and three differentials to power all four wheels. Conceptually similar to the Toyota Hybrid Synergy Drive system which powers the Prius, the Lexus driveline has larger components arranged longitudinally (instead of transversely), and two (versus one) electric drive speeds. A trunk-mounted battery pack consisting of 240 nickel-metal-hydride cells stores the electrical energy.

The Mercedes-Benz S400 BlueHybrid's propulsion system prioritizes low emissions and high fuel efficiency over powerful acceleration. Essentially a scaled-up version of Honda's Integrated Motor Assist, this new Mercedes powertrain teams a 3.5-liter Atkinson-cycle V-6 with a compact AC motor-generator bolted securely to the crankshaft and a ZF seven-speed automatic transmission. The ring-shaped motor-generator is nearly a foot in diameter but less than two inches thick. The Atkinson cycle, a common hybrid technology, uses late closing intake valves to stretch the expansion (power) stroke for utmost efficiency. While some torque is sacrificed with this approach, the S400's electric motor supplies up to 118 lb-ft to more than cover that loss. The S-class's most notable distinction is the hybrid world's first lithium-ion battery system. Thirty-three cylindrical cells supplied by the French firm Saft are housed in steel container mounted under the hood. (The Tesla Roadster is powered solely by lithium-ion batteries with a similar, but smaller, cylindrical configuration.)

Both of these hybrid systems employ engine shut down at stop lights, regenerative braking, and a 130-mph speed governor to curb consumption. While the Lexus has all-wheel drive as standard equipment, that capability is not offered by Mercedes-Benz.

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