Mercedes S400 Hybrid

It might look like an ordinary S-Class, but make no mistake, because the 2010 Mercedes-Benz S400 BlueHybrid represents a major step in the development of the hybrid luxury car.

This prototype is Mercedes-Benz's belated answer to the Lexus LS 600h L — a gasoline-electric hybrid that delivers a combined 299 horsepower along with average fuel consumption just shy of 30 mpg. It also heralds some of the most advanced battery technology ever applied to a series production car.

Don't hold your breath waiting for it, though. With Mercedes-Benz yet to complete development, North American sales aren't planned to get under way until September 2009.

As Seen in Frankfurt
You'll have already heard about the 2010 Mercedes-Benz S400 BlueHybrid from last year's Frankfurt Motor Show, where it was hailed as the forerunner of a whole range of new hybrid models being prepared by Mercedes-Benz. In fact, the hybrid drivetrain and battery pack have been developed along a modular basis, meaning they can easily be altered to suit individual models.

Mercedes-Benz acknowledges it's playing catch-up in the hybrid ranks, and project leader Oliver Vollrath tells us, "The S400 BlueHybrid is not the definitive answer to the world's long-term sustainable mobility requirements. But it does represent a big step into the future, particularly in the area of battery technology. At the moment there is no car that matches its level of technology."

You will recognize the basics from the existing Mercedes-Benz S350. Unlike the more familiar hybrid models from Lexus, however, the S400 BlueHybrid does not possess an ability to run exclusively on electric power. Instead its electric motor is used as a mechanism to permit stop-start operation of the V8 engine for improved fuel economy in stop-and-go driving, then adds a boost of power if required at cruising speed.

A Little Bit of Science
The naturally aspirated 24-valve 3,498cc V6 gasoline engine sitting up front has received a number of revisions, but it oddly does without direct injection. A new cylinder head, revised pistons and modified camshaft improve fuel economy and also raise this V6's power output to 279 hp, some 7 hp more than before. The engine is also rated at 258 pound-feet of torque.

These figures are nothing to write home about, since the direct-injection 3.5-liter V6 found in the CLS350 available in Europe delivers 12 hp and 11 lb-ft more. But the addition of an electric motor, neatly packaged at the front of the gearbox, helps provide added thrust in a car that tips the scales at 4,310 pounds.

With a potential of 20 hp and an ability to serve up 118 lb-ft of torque the moment you hit the accelerator, the circular three-phase AC unit provides the S400 BlueHybrid with a combined output of 299 hp and 284 lb-ft of torque, all of which is transferred to the rear wheels via Mercedes-Benz's seven-speed automatic gearbox and a final-drive ratio of 3.07:1.

Battery Technology
Mercedes-Benz has dug deep into its development budget to deliver a powerful yet lightweight battery pack for the S400 BlueHybrid. It features newly designed high-voltage lithium-ion cells and an associated cooling system.

The Mercedes-Benz battery solution has been engineered specifically for the demands placed upon it by everyday driving, with a new nickel/cobalt/aluminum chemical process that is claimed to provide significant efficiency and energy density gains over the nickel-metal hydride batteries that are used in just about every existing hybrid on the market today. Mercedes-Benz claims the advanced new cells used in the S400 BlueHybrid provide a much faster charge process, additional range and an overall increase in electrical efficiency.

Another advantage is the compactness of the battery design. Instead of sacrificing trunk space like many rivals, Mercedes-Benz has managed to mount its new lithium-ion battery pack (which consists of five separate cells in a high-strength steel casing) underneath the hood. It's located at the base of the windscreen in the place usually taken up by the standard S350's lead-acid unit, which it replaces.

Mercedes-Benz has developed an electronically controlled cooling process integrated into the air-conditioning system that keeps the S400 BlueHybrid's battery cells operating at an optimal temperature of between 59 and 95 degrees Fahrenheit. Altogether, the battery and cooling system uses 25 unique patents. Vollrath claims the batteries will be good for up to 600,000 cycles, or a life of over 10 years.

Mild Driving
As you'd expect from a mild hybrid, the V6 gasoline engine switches off when you touch the brakes and roll to a standstill at speeds below 10 mph, and then automatically restarts again the moment you depress the accelerator. Still, if the S-Class had its hybrid badges deleted, you might just think you were driving a standard S350 with a particularly lively engine.

When we drove a prototype version of the new sedan around the hills of Stuttgart not far from Mercedes-Benz's headquarters in Germany, there were only subtle hints to its advanced drivetrain. The best thing about the S400 BlueHybrid is its seamless power delivery. There might be two different power sources at work, but the way they come together to provide one long, linear surge of hushed acceleration, with just a distant hint of V6 growl if you've really got your right foot planted, is deeply impressive.

Acceleration is brisk, but this is no performance car. Put that down to added weight brought upon by the electric motor, lithium-ion battery pack and associated hardware, all of which add 165 pounds to the car. Mercedes-Benz claims the S400 BlueHybrid accelerates to 100 km/h (62 mph) in 7.2 seconds, just 0.1 second quicker than the S350.

Where it really begins to makes sense, though, is at the gas station. With combined fuel consumption on the European cycle of 29.8 mpg, the S400 BlueHybrid betters the S350 by 7 mpg — enough to provide a 165-mile boost in cruising range from its large 23.8-gallon tank to 708 miles.

Mercedes Does Hybrid Think
The S400's stop-start system is ultra-quick to respond and doesn't impede progress at traffic lights. Steering and air-conditioning also remain functioning, as they've been modified to run exclusively on electricity. The regenerative brakes don't win any awards for feel, though, as the transition from regen mode to mechanical braking still feels unnatural.

For all its low-speed theatrics, it is on the open road where the S400 BlueHybrid feels most at home. This is an S-Class, after all. And since the battery pack and electric motor represent a negligible weight increase, there's no apparent change in this car's dynamic capabilities. The multilink suspension with air springs delivers a comfortable ride, although it doesn't lower its ride height automatically at speed like the Lexus LS 600h L. There's also very little tire roar from these low-rolling-resistance 225/45R18 Continental Contact tires.

Inside, there's little to distinguish the S400 BlueHybrid. An altered instrument display keeps tabs on the flow of electricity in and out of the lithium-ion battery pack, and there is a small hybrid badge on the center console. Otherwise, it is business as usual: acres of space, supreme seating comfort, a near perfect driving position and the famed Mercedes refinement.

Reinventing the Mild Hybrid
For all the buzz created by the 2009 Mercedes-Benz S400 BlueHybrid prototype, this is simply Mercedes' reinvention of the mild hybrid. Perhaps because Europeans have so little experience with hybrid technology, they're aghast at technology we take for granted in the Chevrolet Malibu Hybrid.

It's also interesting that this car's electric powertrain is portrayed as a useful boost to overall power when it's clear that its impact on acceleration is minimal. At the same time, the S400 BlueHybrid does offer a useful improvement in fuel economy, and it suggests that mild hybrids might be the quickest, most affordable technology to improve fuel economy in conventional vehicles.

The good news is that the S400 BlueHybrid is just as good as an S350 in most respects. We'll see what kind of reception it gets when it's introduced in the U.S. in September 2009.