The Mercedes S-Class has been treated to an efficient plug-in hybrid makeover. With a 90-kW electric motor supporting its gasoline V6 engine, Mercedes says the 560e blends in-town efficiency with the power and range to cruise the autobahn.

Plug-in hybrid powertrains are becoming increasingly common in large, luxurious cars like the S-Class, because they allow manufacturers to deliver seriously impressive fuel economy figures on test cycles without forcing drivers to change their fueling habits too much. Their real-world efficiency rarely matches the on-paper promise, but with a bit of careful charge-planning and a light right foot, a big plug-in car should deliver some handy fuel savings for drivers.

In the S650e, electric power comes from a motor with 90 kW of power and 441 Nm (325 lb-ft) of torque. Thanks to the 13.5-kWh lithium-ion battery pack, the car has an electric range of 25 mi (40 km). Even though it holds around 50 percent more juice than the unit in the old S-Class hybrid, the new battery is smaller, freeing up space in the boot.

The gasoline engine is a three-liter V6 making 362 hp (270 hp) of power and 369 lb-ft (500 Nm) of torque. The 60-mph (97-km/h) sprint takes 4.9 seconds, and top speed is limited to 155 mph (250 km/h). No efficiency figures have been given just yet.

To help owners extract the best possible efficiency from the hybrid powertrain, Mercedes has built an Eco Assist feature into the S650e. Depending on how much charge is stored in the battery, the car is always calculating whether it should be coasting in neutral or pulling power back into the battery when the driver lifts off the throttle, and the throttle pedal now provides haptic feedback to signify when maximum e-power is being drawn.

In essence, that means the driver needs to push beyond a clearly defined point to activate the gasoline engine, making it easier to stick exclusively to electric power. The navigation system tells drivers when there's a junction or hill coming up, encouraging them to step off the throttle earlier and save more fuel, while an in-dash display indicates how much time has been spent on pure electric power as a form of motivation.

Aside from the clever gasoline-electric powertrain, the S650e is a standard S-Class. That means it's handsome on the outside, and ultra-luxurious on the inside. The twin-screen setup on the dashboard has been evolved, and the new steering wheel improves on the dual-touchpad design of the E-Class. There are 64 different ambient lighting options, and all the materials are top-notch.

The S650e debuted at the Frankfurt Motor Show, but it won't be on sale in the US until 2019.

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