2010 Mercedes-Benz S400 BlueHybrid - Future and Availability - First Drive

The new speedometer display also shows battery charge. I tried running down to the bottom of a steep, twisting hill, which charged it right up. I then turned and gunned the S-Class back up for a few miles, but the charge state didn't fall far or fast. Every time I touched the brake pedal for a corner, it would regenerate. So it's hard to envision a situation where it would be low. But if it were, the car would proceed happily, just with a little less performance than normal, until it was recuperated again.

The electric motor is just a couple inches thick, sandwiched between the engine and torque converter of the largely unaltered seven-speed transmission. But the transmission software is amended to get optimum shifts points and shift quality with the new powertrain.

The trans also gets its own electric oil pump for the times the engine isn't running. The air-conditioning has an electric pump, too, and the steering also becomes electrohydraulic. That way they all function when the engine is stopped.

At the moment, there's still an alternator and small 12V battery, but engineers say it's likely future iterations of the system will dispense with those two components entirely. They're really only backup: The 12V ancillaries mostly run from the lithium-ion high-voltage battery via an inverter.

Mercedes has built some 100 prototypes of the BlueHybrid, and they're still in durability testing. But the firm is confident the performance figures are final.

The car goes on sale in Germany in June 2009 and the U.S. in September. By then the whole S-Class range will have had a mild facelift.

Daimler chief Dieter Zetsche told me a few weeks back the car's fate had changed with high gas prices. "At first, I thought it was just a marketing tool, just so we could say we had a hybrid. Now it's hard to tell." Interest has been high. "But I'm not sure I want to sell too many, given the cost of it to us. Our intention is to ask the customer to participate in that cost."

In other words, it'll be more expensive than a regular V-6 S-Class in Europe, but still a loss-leader for Benz to ramp up the new technology. Beyond that, at this stage everyone at Mercedes has sealed his lips on pricing.