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PHEV, MHEV or Stromer: That's how efficient the three Mercedes are

The electric motor alone does not make plug-in and mild hybrids economical. Efficiency starts with the driver - this is also shown by the 2,000-kilometer test drive in the footsteps of the efficiency record holder Vision EQXX with the Mercedes C300e and C300d from Stuttgart to Cassis - and back.

The good old V-belt is probably one of the most underestimated comfort features in the car. Because without it there would be no infotainment, no air conditioning, no starter and not even electric windows - or at least you would only have the pleasure of using them for a short time. Because without an alternator and devices such as the air conditioning compressor, comfort is not far off - and many combustion engines are still driven by belts. The problem with belt-driven ancillaries: they only work when the engine is running. Consumers thus ensure a base load in the system and generate a correspondingly poor degree of efficiency - especially if they work in traffic jams and the combustion engine is running in inefficient areas.

Recharging via recuperation instead of an alternator

The solution: not only electrify the drive, but also as many ancillary units as possible. This is what happened with the Mercedes C300e and C300d , where only the water pump is still attached to the belt. "The rest is electrified," explains Mercedes developer Paul Wenzel. Because the two plug-in and mild hybrids even do without the classic alternator. The batteries are charged directly via recuperation, when braking, driving downhill or when the system detects a vehicle driving ahead.

This story is part of a big test on the tracks of the Mercedes EQXX . With the question of which drive is the cheapest and most efficient, we drove like the Vision EQXX efficiency car for its record drive 1,000 kilometers to the French coast to Cassis - and back again. We accompanied the journey with measurements and calculations on the subject of costs, efficiency, consumption and CO₂ emissions. You can find all the details and results of the trip in the auto motor und sport issue 18/2022 .

Only 3 percent of the energy for the air conditioning

With pure electric vehicles like the Mercedes EQE 350+, which has also unwound the 2000 kilometers to the French coast and back to Sindelfingen, the electrification of the units is the case due to the system - on After all, belts on the electric motor wouldn't make any sense. As the data analysis of the e-car shows, only nine to ten kWh of the total of 310 kWh that the EQE required for the entire journey was used for the air conditioning. For comparison: Simple combustion engines tend to consume 0.5 liters more due to the air conditioning, which corresponds to an energy content of around five kWh - but per 100 km. Extrapolated to the total distance, that would be about 10 times more than with an electric car.

The EQE was able to use almost 94 percent of the total amount of energy for the drive, a little over three percent went to the 12-volt on-board network, which operates navigation systems, fans or window regulators, for example. "The ancillary units of the two hybrids, which benefited from the 48 and 400 volt on-board electrical systems, the recuperation and their batteries, should have consumed similar kWh," says Paul Wenzel with certainty. Because both the 100 kW electric motor of the PHEV and the 15 kW integrated starter generator (ISG) of the diesel, which can be used both as a starter and as a booster and to shift the load point of the combustion engine, ensure every braking operation for fresh energy.

Efficient use of technology is important

So that the electrified systems can work really efficiently, the considered use of consumers is important. What the data evaluation of the EQE also shows: If the passenger compartment is very hot and the air conditioning is running at full speed, the air conditioning compressor’s start-up power of 1,500 watts under extreme conditions such as outside temperatures of around 36 degrees is not uncommon and reduces efficiency on short journeys. If the journey takes longer, the system settles in and can maintain the set temperature using less energy. With the EQE, we came up with consumption of around 400 watts for all drivers.

That's why you should think carefully about whether it's really necessary for the air conditioning or heating to change the temperature quickly, especially for short journeys of a few kilometers. For a few degrees more or less to the target, three percent quickly becomes eleven percent in the energy balance for air conditioning - even with the economical EQE and without a V-belt.


Electrification makes cars more efficient - not only if the electric motor provides propulsion. Conventional combustion engines can also keep their fuel consumption in check with electrified auxiliary consumers. However, this makes it even more relevant that the systems are considered and used sensibly, otherwise the full potential of the technology is gone again.


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