"By 2017 we'll have ten plug-in hybrids models across our range," said Professor Thomas Weber, a board member at Daimler, and the man responsible for development.

It started with the biggest Mercedes car, the S class S 500 Plug-In Hybrid, the one that launched the serial use of this technology. But it was not lonely for long. Soon it was joined by the second in the line of plug-in hybrids, a lot smaller yet no less eco or powerful, the C 350 Plug-In Hybrid. By now, the third one has emerged: the GLE 550 Plug-In Hybrid, and there are seven more coming. GLE and S combine the electro engine with bigger, more powerful motors, whereas a four-cylinder, 211 horsepower 2.0 liter turbo engine is used in the Mercedes C class. Why is that important?

Simple: such a drivetrain will be used in even smaller models, the A and B classes. Also, a C with an even bigger hybrid powertrain would be simply too expensive, and the battery too large. Mercedes is well aware that competition, in the form of BMW's series 3, will soon be on the market, as well as Audi's A4 with a plug-in hybrid powertrain. BMW 3 already exists as a prototype, while Audi announced the issue of Q7, A6 and A8 before the A4. There is, however, no doubt that the A4 will arrive as a plug-in hybrid, maybe with the same powertrain as the Passat GTE (Audi A3 e-tron sportback has the same powertrain as Golf GTE). Passat has longer electric range than Mercedes (you can learn more about it in this issue of Plugin Magazine). Nevertheless, Mercedes C is the first on the market, and that is very important for potential buyers.

Why a smaller battery? When designing batteries, the technology must be kept in mind, as battery size could easily would get in the way of trunk space (especially if the engineers strive for big capacity). Other compromises are also possible, like creating a smaller petrol tank.

C 350 Plug-In Hybrid has a shallower trunk than the regular class C. To compensate, the engineers created a handy compartment on the side of the trunk, where you can store the charger that is meant for home charging and that is, in these type of cars, quite large, due to its control electronics. If you are resourceful, the compartment can be used to store a cable with Type2 plug-ins, for charging at charging stations. Such solutions that keep your trunk tidier more than compensate for the loss of a few liters of volume. Besides, the cable is a spiral, and therefore does not tangle. It is, however, true that it could be a bit longer. The charger is under the hood that is on the rear bumper, and can get pretty dirty, but it is luckily easily opened and closed with just one touch.

The battery that takes up all that trunk space is lithium-ion with 6 kWh capacity. It weighs around 100 kg (due to a liquid cooling system, for better endurance) and has enough electricity for 31 km, according to ECE standards. The truth is that, when the air conditioning is on, the conditions are not ideal, and the expected range drops to between 24 and 26 km. Mercedes engineers did not only focus on the range of the car, which is proven by the fact that, despite the low capacity of the battery compared to their competition (some plug-in hybrids have batteries that are twice the size), they found ways to further improve the car's performance.

A 211 horsepower, four-cylinder turbocharged petrol engine, when added to an electric engine with 60 kW and 80 hp, adds up to 279 hp. As it is capable of 600 Nm of torque, more than is typical of diesel models on the market, it's clear that, when you floor the gas pedal, this C class car kicks you in the back. The electric engine is installed between the clutch and the automatic transmission, and offers four classic transmission modes: e-mode (the petrol engine still kicks in if the gas pedal is fully pressed), hybrid mode, e-save and charge. The C 350 Plug-In Hybrid runs on electrical power alone, as long as the battery is more than 10% full. After that, it can run in hybrid mode until the battery is down to 5%.

It's interesting to drive in hybrid mode in Eco mode (the other possibilities are Comfort, Sport and Custom): based on data from the navigation system, if the destination is set, the car can change driving modes to make the drive most efficient, and use only electricity for town driving. With the help of the cruise control's radar, even when it is turned off, the car monitors road action in front of the vehicle and, with two short pumps of the gas pedal, reminds the driver to adjust the speed, so as to make the drive as efficient as possible. Excellent. There are, of course, standard safety technologies included, like attention assist, collision prevention assist (which works at speeds up to 200 km/h) and AirMatic air suspension.

In a nutshell: the C Plug-In Hybrid proves that diesel cars are no longer needed, as it is just as economical in town as it is on long distance drives. Despite its 1780 kg (which is about 250 kg more than the petrol-powered C 300, with 3 times its consumption), it can be as fast as a sports car. But that's not the point, is it?

Nov. 6, 2015 Driving photo: Saša Kapetanović

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