New Mercedes-Benz plug-in hybrids: The technology behind the compacts

The press driving presentation of the A 250 e (Kraftstoffverbrauch kombiniert 1,5-1,4 l/100 km, CO2-Emissionen kombiniert 34-33 g/km, Stromverbrauch kombiniert 15,0-14,8 kWh/100 km*) and the B 250 e (Kraftstoffverbrauch kombiniert 1,6-1,4 l/100 km, CO2‑Emissionen kombiniert 36-32 g/km, Stromverbrauch kombiniert
15,4-14,7 kWh/100 km*) marks the end of a development phase that began for me in 2014, when I helped to define the requirement specifications for the hybrid drivetrain. During this time, we made several difficult decisions, which fortunately proved to be correct.

Customers will soon be able to order the first plug-in hybrids (PIH) of our compacts: the A 250 e and the A 250 e sedan (Kraftstoffverbrauch kombiniert 1,4 l/100 km, CO2‑Emissionen kombiniert 33-32 g/km, Stromverbrauch kombiniert 14,8 -14,7 kWh/100 km*). Sales of the B 250 e will start a few weeks later, and additional models are already in the pipeline. In this way, we can boost the Mercedes-Benz plug-in offensive, which is labeled EQ Power. It will greatly help us to achieve our goal of offering this drive type in more than 20 model variants from all vehicle segments in 2020.

Kraftstoffverbrauch kombiniert 1,4 l/100 km, CO2‑Emissionen kombiniert 33-32 g/km, Stromverbrauch kombiniert 14,8 -14,7 kWh/100 km* A 250 e Limousine. The A-Class during the press drive in Stuttgart

Our new compact hybrid models primarily distinguish themselves from the competition in three ways.

  • Depending on how the car is driven and equipped, the new hybrid models can travel up to 75 kilometers solely on electricity.
  • They can reach speeds up to 140 km/h solely on electricity.
  • Our customers don’t have to make any noticeable sacrifices with regard to space.

Clever packaging and an innovative exhaust system

How did we do that? A number of decisions were crucial here.

  • The plug-in hybrid transmission is very compact (see below for the details concerning the hybrid traction head).
  • The battery is larger and the electric machine is more powerful than originally planned. We made these improvements in close interaction with the model series. An unusual idea made it all possible: The combustion engine’s exhaust system does not extend to the end of the vehicle, as usually. Instead, it ends in the middle of the car between the two front seats. Moreover, the rear muffler was moved into the transmission tunnel. .
  • In combination with the transfer of the fuel tank into the rear axle area, this move creates space under the rear seats for a high-voltage battery. As a result, the luggage compartment is only slightly smaller than that of the non-hybrid sister models. Nevertheless, the battery is large enough so that the vehicle can travel a considerable distance when it runs solely on electricity.

Kraftstoffverbrauch kombiniert 1,5-1,4 l/100 km, CO2-Emissionen kombiniert 34-33 g/km, Stromverbrauch kombiniert 15,0-14,8 kWh/100 km* A250 e. Kraftstoffverbrauch kombiniert 1,4 l/100 km, CO2‑Emissionen kombiniert 33-32 g/km, Stromverbrauch kombiniert 14,8 -14,7 kWh/100 km* A 250 e Limousine. Using a 7.4 kW wallbox with alternating current (AC), the battery is charged in 1 h 45 min from 10-100 percent SoC (Status of Charge). In DC charging, the charging time is about 25 minutes from 10 to 80 percent SoC

The innovative packaging concept did raise a few questions, of course, but fortunately we could answer all of them satisfactorily. Can such a solution be approved for road use? Yes, it’s not a problem in most of the markets in which we plan to sell our compact models as EQ Power vehicles. Does it make it hard to service the vehicle? No. And, thirdly, does it have a negative impact on the noise level? Appropriate measures enabled us to solve this problem as well.

The technical data and some background information

The engines of the Mercedes-Benz compact vehicle family are installed transversely. For the dual-clutch transmission 8F-DCT, we developed a compact hybrid traction head that is based on the same technical principles as its counterpart in vehicles with longitudinal engines. The component is a permanently excited synchronous machine that operates as an internal rotor. The stator is firmly integrated into the traction head housing. The low-loss wet engine separator clutch is installed in the electric machine’s rotor. A needs-based stator and rotor cooling system makes it possible to easily use the electric machine’s constant and peak power outputs.

The electric range is, depending on the model and equipment, over 70 km

The system’s electrical energy storage unit is a high-voltage lithium-ion battery with a total capacity of approximately 15.6 kWh. The battery can be recharged from an external energy source. The battery comes from Deutsche ACCUMOTIVE, a wholly owned subsidiary of Daimler. The battery is water-cooled and weighs about 150 kg. The A 250 e and the B 250 e can be recharged with alternating or direct current. A corresponding combination vehicle socket can be found on the right-hand side of the new hybrid models. At a 7.4 kW wallbox, the compact plug-in hybrids can be recharged with alternating current (AC) from 10 to 100 percent SoC (Status of Charge) in 1 hour and 45 minutes. The charging time for DC charging amounts to 25 minutes for 10 to 80 percent SoC, for example.

A high system output for great driving pleasure

The electric machine generates 75 kW. Combined with the 1.33-liter four-cylinder engine, this translates into a system output of 160 kW (218 hp) and a system torque of 450 Nm. Thanks to the electric machine’s EQ Power, the A 250 e and the B 250 e respond very quickly when the driver steps on the accelerator. The driving performance is remarkable: For example, the A 250 e only needs 6.6 seconds to accelerate from 0 to 100 km/h. It has a top speed of 235 km/h. The surprised feedback that I often get from colleagues who travel in an electric A-Class for the first time is simply “Wow”! Of course we hope that customers will respond that way too.

On hot days this summer, we were already elated as we got into the cars, because our PIH compacts are equipped with an electric refrigerant compressor. This enables the vehicles to be air conditioned before you even turn on the motor. The auxiliary climate control system can also be conveniently activated by smartphone.

Kraftstoffverbrauch kombiniert 1,5-1,4 l/100 km, CO2-Emissionen kombiniert 34-33 g/km, Stromverbrauch kombiniert 15,0-14,8 kWh/100 km* A 250 e. Kraftstoffverbrauch kombiniert 1,4 l/100 km, CO2‑Emissionen kombiniert 33-32 g/km, Stromverbrauch kombiniert 14,8 -14,7 kWh/100 km* A 250 e Limousine

Another innovation: starting without a starter

For the first time at Mercedes-Benz, the engine is started exclusively by the electric machine. In fact, the compact hybrids don’t even have a separate 12-volt starter, as is the case with the other hybrid models. It was an exciting moment when we made the first cold start using only the high-voltage system. It worked exactly as we had predicted, although it occurred at -25 degrees Celsius in a cold storage unit in Finland.

When you start the vehicle, you immediately notice that our plug-in hybrids primarily run on electricity. When the start button is pressed, the vehicle “comes to life” without making any noise. The word “READY” appears in the display to let the driver know that the drive system is on. “Why isn’t the engine starting?” colleagues often asked during the first test drives in A 250 e preproduction vehicles.

We quickly explained that the engine only kicks in later. The normal drive-off mode is electric. The combustion engine isn’t started until more output is needed than the electric motor can provide or when the battery is becoming depleted. This has never happened on the route I drive to and from work every day. This route extends from the Fildern region to Sindelfingen, a distance that the A 250 e can easily cover without producing any emissions.

As sophisticated as the big cars

Our compact vehicles use the technology of the third generation of plug-in hybrids of the current S-Class, E-Class, and C-Class cars. The systems have been scaled to the compacts and include the power electronics, the high-voltage battery, the 7.4 kW AC charger, and the software. As a result, all of these functions are also available for the compacts. One of these functions is the smart route-based operating-mode strategy, which takes the navigation map data, speed limits, route, and other factors into account. After examining the entire planned route, the operation strategy suggests which stretches are especially suitable for electric driving. The system also reduces the vehicle’s speed in good time before a place-name sign is reached and saves up enough electrical range if the intended destination is in a downtown area.

Kraftstoffverbrauch kombiniert 1,4 l/100 km, CO2 Emissionen kombiniert 33-32 g/km, Stromverbrauch kombiniert 14,8 -14,7 kWh/100 km* A 250 e Limousine

MBUX drive programs let the driver decide

The A-Class pioneered our MBUX (Mercedes-Benz User Experience) system. That’s why the A 250 e also features the new drive programs Electric and Battery Level from the very start. The Electric mode enables the driver to achieve maximum electric performance. In this mode, the combustion engine is only activated when the driver puts the accelerator in kickdown position. The Electric program also lets the driver select the rate of energy recovery by pressing the paddles behind the steering wheel. Five different recuperation levels are available (DAUTO, D+, D, D-, and D–).

The other driving modes are Comfort, ECO, and Sport. Since the introduction of MBUX, all of the EQ Power models have incorporated the previous plug-in operating modes into the drive programs. By selecting the respective program, the driver can either prioritize electric driving (Electric mode), emphasize dynamic handling by using both drive systems (Sport), or focus on combustion-engine driving in order to save up the vehicle’s electric range, for example (Battery Level).

The battery can be charged not only from household power networks, e.g. at a Mercedes-Benz Wallbox, but also easily and conveniently while traveling. MBUX helps the driver find charging stations. Because the MBUX system understands normal forms of speech, it’s possible to start the search function by simply saying, “Hey Mercedes, find nearby charging stations.” Payment via Mercedes me Charge is also extremely easy.

The most important messages conveyed by the A 250 e and the B 250 e might be: Driving electrically is very easy — and fun!

*Die angegebenen Werte sind die ermittelten „NEFZ-CO2-Werte“ i.S.v. Art. 2 Nr. 1 Durchführungsverordnung (EU) 2017/1153. Die Kraftstoffverbrauchswerte wurden auf Basis dieser Werte errechnet. Die Reichweite und der Stromverbrauch wurden auf der Grundlage der VO 692/2008/EG ermittelt. Als Bemessungsgrundlage nach dem EmoG ist ein anderer Wert maßgeblich. Als Bemessungsgrundlage für die Kraftfahrzeugsteuer kann ein höherer Wert maßgeblich sein.

Weitere Informationen zum offiziellen Kraftstoffverbrauch und den offiziellen spezifischen CO₂-Emissionen neuer Personenkraftwagen können dem „Leitfaden über den Kraftstoffverbrauch, die CO₂-Emissionen und den Stromverbrauch“ neuer Personenkraftwagen entnommen werden, der an allen Verkaufsstellen und bei der Deutschen Automobil Treuhand GmbH unter unentgeltlich erhältlich ist.

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Felix Ascher works at the Powertrain unit, where he is responsible for the plug-in variants of compact vehicles. Ascher, who has a degree in engineering, already worked on hybrid transmissions and hybrid vehicle concepts as a trainee. Beginning in 2014, he helped to define the requirement specifications for compact hybrids. He joined the project team a year later.