At the Geneva Motor Show this week, Mercedes-Benz is unveiling two new preproduction models that combine the new OM 654 four-cylinder diesel engine with the latest-generation 9G-TRONIC 9-speed hybrid transmission. Like the S 560 e (combined fuel consumption 2.1 l/100 km (112 mpg US), combined CO2 emissions 49 g/km) (earlier post), the C- and E-Class plug-in diesel hybrids will use third-generation hybrid technology.
The projected key points are 90 kW electric output, an additional electric torque of 440 N·m and an electric range of around 50 km in the NEDC. This is made possible in the third hybrid generation also by the new lithium-ion battery, which can store 13.5 kWh of energy. The new on-board charger doubles the charging rate from 3.6 kW to 7.2 kW.
A discharged battery can thus be fully recharged in two hours at a wallbox. This is possible within around seven hours even at a conventional domestic power socket. The company is also introducing an intelligent, connected variant of the Mercedes‑Benz wallbox to enable easier charging while offering a series of additional functions via a new app.
The third-generation hybrid technology supports the driver with further improved, intelligent drive management. Through the extended use of data from the navigation system and information from the camera and the radar sensor, 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 drive components.
In addition to a superlative driving experience with a total torque of 700 Nm, available from as low as 1400 rpm, the new plug-in diesel hybrids will offer added comfort. The high-voltage on-board electrical system supplies not only the powertrain components, 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.
OM 654 diesel. The new plug-in diesel hybrids in the C- and E-Class will share the new OM 654 four-cylinder diesel engine. (Earlier post.) This is the first passenger car diesel engine to use the stepped-bowl combustion process—named after the shape of the combustion bowl in the piston. The innovations also include the combination of an aluminium engine block and steel pistons, as well as the further-improved NANOSLIDE coating of the cylinder walls. The internal friction has been reduced by around 25%. The new engine also benefits from the use of fourth-generation common-rail injection with pressures of up to 2050 bar.
In addition, the engine is also more compact than its predecessor. All components relevant for efficient emissions reduction are installed directly on the engine. Thanks to the near-engine configuration, exhaust aftertreatment has a low heat loss and excellent operating conditions.
ECO Assist. The new hybrids provide the driver with comprehensive assistance in terms of predictive driving and fuel-saving: the driver is prompted when appropriate to come off the accelerator, e.g. because the S-Class is approaching a speed limit, and assisted by innovative functions such as coasting and energy recovery. For this purpose, navigation data, traffic sign recognition and information from the intelligent safety assistants (radar and stereo camera) are linked and processed.
ECO Assist takes the following traffic situations and information into account in its driving recommendations and efficiency strategy:
- Route profile (bends, junctions, roundabouts, gradients)
- Speed limits
- Distance from vehicles ahead
ECO Assist continuously generates coasting simulations in the background: depending on the state of charge of the battery and the traffic situation, it computes whether the vehicle should ideally be allowed to coast with the lowest possible driving resistance with the driver's foot off the pedals, or whether it should be decelerated so that the battery can be efficiently charged (energy recovery).
The haptic accelerator helps the driver to achieve an economical and comfortable driving style. A variable pressure point in the pedal, for example, tells the driver that the maximum electric power is being delivered. If the driver continues to press the pedal beyond the pressure point, the combustion engine kicks in. A perceptible resistance in the haptic accelerator advises the driver to take their foot off the accelerator. If the driver follows this recommendation, the combustion engine is switched off and decoupled from the powertrain.
Within the limits of the system, ECO Assist controls the overrun mode according to the situation as soon as the driver takes their foot off the accelerator. The driver is also given a visual prompt to do this: by a “foot off accelerator” symbol in the central display (or, if installed, in the head-up display). At the same time, a diagram gives the driver the reason for the recommendation (e.g. “Junction ahead” or “Gradient ahead”).
To increase the driver’s motivation to follow the recommendations of ECO Assist, the on-board computer records how many kilometres/for how much time during a journey the car was driven with the engine off, and shows this in the central display. The reward not only takes the form of reduced fuel consumption, but also an increased electric range.
Four hybrid modes. Four operating modes can be preselected:
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.
Third-generation hybrid drive. The third-generation hybrid transmission is based on the 9G-TRONIC automatic transmission. The torque converter, clutch and electric motor are housed in the hybrid drive unit. The compact design was achieved by integrating and connecting the separating clutch, torsional vibration damper and torque converter lockup clutch within the rotor of the electric motor. The torque converter with its powerful and highly efficient hydraulic circuit offers smoothness when pulling away in hybrid mode.
Developed together with Bosch as part of the EM-motive joint venture, the electric motor was specially designed for the 9G-TRONIC plug-in hybrid transmission. The equally new power electronics have allowed further increases in output and torque compared with the second generation. The electric performance of 90 kW and 440 Nm contributes to an effortlessly superior driving feel. The top speed in e-mode has been raised from 130 km/h (81 mph) to 140 km/h (87 mph).
A key factor in the increase of the electric range to around 50 kilometres is the nominal capacity of the new lithium-ion battery, which has grown to 13.5 kWh, while the size of the battery has remained 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.
Delivery of the first models is scheduled for late summer 2018. At the moment, the company is making systematic preparations for series production of the new plug-in hybrids, with its engineers taking the last important steps on the way to the start of production.