Under the microscope: Driving more efficiently: Intelligent co-pilots

2019 will be the year of the plug-in hybrid at Mercedes-Benz: Over the course of the year, the range will be expanded to well over ten model variants in the most important segments – from the compact car to the S-Class. And in the SUV segment so popular with customers, Mercedes-Benz is going on the offensive as well. Alongside the Mercedes-Benz GLC as a plug-in hybrid is the new generation of the Mercedes-Benz GLE just introduced on the market and ready and waiting for 2019. Customers in the compact car segment can also look forward to initial electrified variants still before the year is out.

Plug-in hybrids offer customers the best of both worlds: in town they run in all-electric mode, while on long journeys they benefit from the range of the combustion engine. They make the vehicle more efficient overall because they can firstly recover energy and ly allow the combustion engine to run in favourable operating ranges. EQ Power is also a guarantee of exceptional dynamism. EQ Power+ is the name of the performance hybrid technology that Mercedes‑AMG will use on the road in future and is already used successfully in Formula 1 today.

Mercedes-Benz is the only manufacturer to also combine the diesel engine with plug-in technology. Third-generation plug-in hybrids can contribute to better air quality in cities and represent a key technology on the road to the emission-free future of the automobile: With an all-electric range of around 50 km and an electric motor output of 90 kW, Mercedes-Benz SUVs, saloons and estate models are locally emission-free in any inner city. In future, electric range will further increase thanks to bigger batteries.

90 kW electrical output for all plug-in hybrids

The current electric engine has been redesigned for the 9G-TRONIC plug-in hybrid drives and is designed according to the principle of a permanently excited synchronous motor as an internal rotor. The likewise new, significantly enhanced power electronics have allowed significant increases in power and torque density. A peak output of 90 kW and a start-off torque of 440 Nm make for an effortlessly superior driving feel even in all-electric mode and allow top speeds in excess of 130 km/h. The stator is permanently integrated in the traction head housing, while the rotor is between the power flow of the separating clutch and transmission input. On-demand stator and rotor cooling allows use of the electric motor's peak and continuous output without any problems.

More energy stored in greater density, for a longer electric range

All new-generation plug-in hybrids from Mercedes-Benz now boast an all-electric, locally emission-free range of around 50 km (NEDC). A key factor in increasing the electric range to around 50 kilometres is the nominal capacity of the new lithium-ion battery, which has increased to 13.5 kWh, while the size of the battery has been kept the same. The evolution of the cell chemistry from lithium-iron-phosphate (LiFePo) to lithium-nickel-manganese-cobalt (Li-NMC) made it possible for the cell capacity to be increased from 22 to 37 Ah. The highly efficient battery system comes from the Daimler subsidiary Deutsche ACCUMOTIVE. The power electronics are housed in the engine compartment.

On-board charger with 7.4 kW capacity

The new on-board charger more than doubles the charging capacity from 3.6 kW to 7.4 kW and strikes an ideal compromise between size, weight and charging capacity. A discharged battery can thus be fully recharged in 1.5 hours at a wallbox, for example in the convenience of one's own home. The same is possible in around five hours even at a conventional domestic power socket.

Electrical pre-entry climate control for the interior

The high-voltage on-board electrical system supplies not only the powertrain components and the vacuum pump of the regenerative braking system, but also the electric refrigerant compressor and the high-voltage heater booster. Both allow pre-entry climate control of the interior not only in summer but also in winter because they can also operate without the combustion engine.

Intelligent operating strategy: Supporting the driver

Third-generation hybrid technology supports the driver with further-improved, intelligent powertrain management. It comprises all processes that access the on-board energy supply and influence consumption, including the hybrid operating strategy, i.e. the interaction between electric motor and combustion engine, the transmission gear shift strategy, thermal management, i.e. the energy-efficient control of the cooling circuit of the combustion engine and electrical components to maximise the electric range, recuperation management and, in the case of the diesel hybrids, even particulate filter regeneration. Through the extended use of data from the navigation system and information from the camera and the radar sensors, third-generation hybrid vehicles can look ahead well beyond the driver's field of vision and adjust to the specific speed/route profile. Events such as negotiating towns on the way to the destination are taken into account when planning the available electrical energy, and during recuperation and thermal conditioning of the powertrain components. In addition, the ECO Assist helps save energy (see chapter "Drive more efficiently").

Performance to suit the driver's wishes: four hybrid modes

Depending on the driver's wishes, four operating modes can be preselected. They are:

  • HYBRID: Default setting; all functions, such as electric driving, boost and energy recovery, are available and used according to the driving situation and route profile
  • E-MODE: Electric driving, for example in the city centre. The accelerator signals the pressure point at which the combustion engine is started
  • E-SAVE: The charged battery is held in reserve to allow driving in all-electric mode later
  • CHARGE: The battery is charged while driving.

Hybrid traction head in torque-converter transmission: more powerful, more compact

At the heart of the mechanical system in all third-generation plug-in hybrids with combustion engine is the 9G-TRONIC 9-speed hybrid transmission. It augments the familiar nine-speed automatic transmission with torque converter by adding a hybrid traction head with integrated converter, a separating clutch and a powerful electric motor. All of the benefits of the basic transmission are retained, including the exceptional motoring comfort, barely perceptible gear shifts and, in the case of the E-Class, for example, a high towing capacity. The most powerful version of the transmission with a transmissible torque of up to 700 Nm is used for hybrid operation to enable the combined power of the combustion engine and electric motor to be used if required. The exceptionally efficient 9G-TRONIC 9-speed hybrid transmission helps to improve the efficiency of the powertrain, especially in electric mode.

The major benefit of the new hybrid traction head is its compact design, which was achieved thanks to the innovative integration and connection of the separating clutch, torsional vibration damper and torque converter lock-up clutch within the rotor of the electric motor. This results in the transmission being slightly longer than the 9G-Tronic basic transmission, but only by 108 mm.

In contrast to the second-generation traction head, in which the electric motor was connected directly with the transmission input and a wet start-off clutch was used as a starting and separating clutch, a torque converter between the electric motor and the transmission now takes care of starting off. The separating clutch has been improved with respect to drag torque, now that it no longer has to deal with starting off, in order to reduce losses during electric mode.

To optimise vibration decoupling, the hybrid transmission includes two torsional vibration dampers that damp the combustion engine excitations. The first vibration damper is installed between the engine and transmission, while the 2nd is integrated in the torque converter.