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DRIVES: 2010 Mercedes-Benz S400 BlueHybrid

Rafay Ansar

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SPECS
ON SALE: Fall 2009
BASE PRICE: $100,000 (est)
DRIVETRAIN: 3.5-liter, 299-hp, 284-lb-ft V6 with integrated motor assist; RWD, seven-speed automatic
CURB WEIGHT: 4,383 lb
0-62 MPH: 7.2 sec (mfr)
FUEL ECONOMY: 30 mpg

Mercedes-Benz missed North America's move toward hybrids. It was caught sleeping, there was not enough research and development funding, it was too focused on diesels for the European market--pick your reason. It just wasted the opportunity to be a pioneer in the hybrid field. That accolade belongs to Toyota and its Mercedes-rivaling Lexus division, whose serene LS 600h is regarded as the best luxury hybrid thus far.

So, a lot hangs on the new Mercedes S400 BlueHybrid, developed in a joint engineering program with rival BMW, which plans to unveil its version, the 7-series ActiveHybrid, at the Paris motor show. Mercedes is keen to ensure that the S400 BlueHybrid is considered something extraordinary. That's one reason project leader Oliver Vollrath says it has taken so long to reach production. "When you're turning up to the party late, you want to make sure you've got something special to offer," he says.

When it goes on sale in North America in September 2009, the S400 BlueHybrid likely will cost about the same as today's S550. The problem is, to the average shopper, it looks like the three-year-old S350. You can look for aerodynamic amendments or changes in ride height, but you'll be looking in vain. Only subtle BlueHybrid badges on the flanks and the trunk lid signal the high-tech driveline. Keener observers will spot new wheels and tires: 18-inch alloys with low-rolling-resistance Continental Contact 235/55R rubber.

Underneath, a lightly reworked version of the existing Mercedes 3.5-liter V6 gasoline engine gains a new cylinder head, lightweight pistons and a reprofiled camshaft for altered valve timing. It does without the direct injection used on the CLS350's similar V6. Output increases by just 7 hp over the S350, at 279 hp, with torque remaining the same at 258 lb-ft.

Those are not dazzling figures for a car that weighs 4,383 pounds. But a three-phase AC electric motor, mounted within the front of the gearbox housing, provides additional thrust when required. The S400 BlueHybrid's peak output swells to 299 hp and 284 lb-ft, with drive channeled to the rear wheels via the standard Mercedes seven-speed automatic. The new system does not support pure electric propulsion like that offered by the LS 600h; the efforts of the electric motor are used exclusively to assist the gasoline engine.



Mercedes expects that the S400 BlueHybrid's advanced new lithium-ion battery will be the envy of rival carmakers. Weighing 60 pounds and made up of five cells, the battery pack uses a chemical process based on nickel-cobalt-aluminum. This, Mercedes claims, provides more efficient charging and improved discharge properties compared with the nickel-metal-hydride technology used in most hybrids. It also is incredibly compact, so much so that Mercedes has managed to mount the battery in the position usually reserved for the S350's standard lead-acid unit at the base of the windscreen, where it is cooled by a patented process linked with the car's air-conditioning system, keeping it operating within an optimal range between 59 and 95 degrees Fahrenheit.

The battery stores electricity created under braking and when coasting, during which the S400 BlueHybrid's electric motor functions as a generator. Other fuel-saving measures include an integrated stop/start system, in which the gasoline engine switches off when the driver engages the brakes at speeds of less than 10 mph and then automatically restarts when the accelerator is depressed.

The S400 BlueHybrid doesn't demand any change in driving style as some hybrids do. It feels much like the S350, only a touch more powerful under acceleration in lower gears. Around town, the stop/start system works well, the electric motor providing almost instantaneous start-up after the engine has been automatically switched off at traffic lights and such. On the open road in upper gears, the added output is not immediately evident, in part because of the added 165 pounds of the hybrid system. Power delivery is smooth and seamless, with or without electric assist. What stands out is how fast the battery charges; one long, downhill stretch is enough to see it charge at almost 100 percent.

Mercedes claims 0 to 62 mph in 7.2 seconds, just 0.1 second inside the time it quotes for the S350. But the emphasis is not on performance. The S400 BlueHybrid is meant to optimize fuel economy. A claimed combined city/highway average of 30 mpg betters that of the S350 by 7 mpg, yielding a gain of 165 miles in range. Equally impressive is the CO2 rating, which, at 190 grams per kilometer, betters that of its gasoline-only sibling by 57 grams per kilometer.



An electronic display in the instrument panel relays all relevant information, glowing green when the battery is stowing electricity and red when electricity is being used. Another display keeps the driver informed of the state of charge.

A taut chassis and supple suspension are longtime Mercedes traits. The S400 BlueHybrid feels fluid and well balanced despite the added weight, sponging away potholes with poise and control. It can maintain a rapid pace on winding roads and high speeds on the autobahn with stability.

Criticisms? The brakes seem over-assisted, with an uneven feel in the first few degrees of travel, making them hard to modulate. The steering also appears to have lost some inherent directness, with electric rather than traditional hydraulic power assist.

The S400 BlueHybrid feels like a well-engineered car that moves the hybrid game along, thanks largely to its lithium-ion-battery technology, superior to the nickel-metal-hydride technology most carmakers have relied on. But with its me-too looks, Mercedes dealers might have their work cut out for them in trying to lure S-class owners into the showroom. The biggest factor in closing the deal--the price, so that one can cal-culate the payoff in improved fuel economy--won't be available until close to the on-sale date. That's just as well. There's no telling what gasoline might cost by then, and any calculations now would be meaningless.
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