Powertrain: systematic electrification of the modern four-cylinder engines

Thanks to systematic electrification and intelligent downsizing, the new C-Class sets new standards in efficiency. The engine range has only four-cylinder units from the current modular FAME (Family of Modular Engines) Mercedes-Benz engine family. Accordingly, the engine range plays a major role in the flexibility of the international production network, with needs-based electrification.

In addition to turbocharging, both the diesel and the petrol engines now have an integrated starter-generator (ISG) for intelligent assistance at low engine speeds as a mild hybrid of the second generation. This ensures outstanding power delivery. The ISG uses a 48 volt on-board electrical system that ensures functions such as gliding, boosting or energy recovery, and makes significant fuel savings possible. The engines also start very rapidly and comfortably as a result, so that the start/stop function is almost as imperceptible to the driver as the transition from gliding with the engine switched off to strong acceleration under engine power. When idling, the intelligent interaction between the ISG and the combustion engine ensures outstandingly smooth running.

First diesel with an integrated starter-generator

Spearhead of the efficiency improvement measures is the new OM 654 M with an integrated second-generation starter-generator (ISG). It has a 48-volt partial on-board electrical system. An energy recovery function and the ability to "glide" with the engine switched off make the engine even more efficient. Along with electrification, which also includes the use of an electric refrigerant compressor for the air conditioning system, the most important modifications that make an output of up to 195 kW plus an additional 15 kW from the EQ Boost system possible are:

  • A new crankshaft increases the stroke to 94.3 mm and the displacement to 1993 cc (previously: 92.3 and 1950).
  • The injection pressure is increased to 2700 bar (previously 2500).
  • Particularly fast response times and uniform power delivery thanks to two water-cooled turbochargers, both now featuring variable turbine geometry.
  • A sodium-filled cooling duct in each of the steel pistons. This helps to dissipate temperature peaks in the combustion cavity of the pistons.

In terms of exhaust gas aftertreatment, this most powerful of the four-cylinder diesel engines also takes things one step further. Its components include:

  • a close-coupled NOx storage catalytic converter for reducing nitrogen oxides
  • a DPF (diesel particulate filter with special coating for reducing also the amount of nitrogen oxides)
  • an SCR catalytic converter (selective catalytic reduction with metered injected quantity of AdBlue®) and
  • an additional SCR catalytic converter in the vehicle's underbody, with a separately metered injected quantity of AdBlue®

Four-cylinder petrol engine also with a second-generation ISG

The four-cylinder M 254 petrol engine with a second-generation starter-generator with an additional output of up to 15 kW and 200 Nm more torque is also celebrating its première in the C-Class. Thanks to energy recovery and the ability to "glide" with the engine switched off, the petrol engine is highly efficient. In the M 254, Mercedes-Benz has for the first time combined all the innovations of the modular engine family of four and six-cylinder petrol and diesel units in a single engine. They include NANOSLIDE® cylinder coating, CONICSHAPE® cylinder honing (trumpet honing) and the exhaust aftertreatment system positioned directly at the engine.

A completely new feature is the segment charger with flow connection, an advancement of the twin-scroll technology for even more instantaneous response of the forced induction system. The completely newly developed segment turbocharger is a result of cooperation between Mercedes-Benz turbocharger developers and the Mercedes-AMG Petronas Formula 1 team. The technology transfer to series production sets new standards with respect to power combined with maximum efficiency. For short periods, the output of the C 300 (combined fuel consumption: 7.0-6.6 l/100 km, combined CO2 emissions: 159-150 g/km)2 can additionally be increased by up to 20 kW overboost.

Transmission: Automatic now standard across the board

The 9G-TRONIC transmission was developed further for adapting the ISG, and is installed in all C-Class models. The electric motor, power electronics and transmission cooler have now moved into or to the transmission. Previously required lines are eliminated, which offers advantages with regard to installation space and weight. In addition, the efficiency of the transmission has been increased. Amongst other things, the optimised interplay with the electric auxiliary oil pump reduces the delivery rate of the mechanical pump by 30 percent compared with the predecessor – good for efficiency. Furthermore, it uses a new generation of the fully integrated transmission control with multi-core processor and new design and connectivity technology. In addition to the increased computing power, the number of electric interfaces has been drastically reduced, and the weight of the transmission controls have been cut by 30 percent compared with the predecessor.

The 4MATIC drive system of the all-wheel drive models has been advanced. The new front-axle drive allows higher torque levels to be transferred with an ideal axle load distribution for driving dynamics. Moreover, this has a significant weight advantage compared to the corresponding component in the preceding series – a contribution to CO2 reduction. The technicians were also able to reduce the friction losses in the new transfer case. In addition, it also a closed oil circuit, and requires no additional cooling measures.

Overview of Saloon and Estate models[1] (petrol engines):

 

 

C 180

C 200

C 200 4MATIC

C 300

C 300 4MATIC

Displacement

cc

1496

1496

1496

1999

1999

Output

kW/hp

125/170

150/204

150/204

190/258

190/258

at

rpm

5500-6100

5800-6100

5800-6100

5800

5800

Add. output (boost)

kW/hp

15/20

15/20

15/20

15/20

15/20

Peak torque

Nm

250

300

300

400

400

at

rpm

1800-4000

1800-4000

1800-4000

2000-3200

2000-3200

Add. torque (boost)

Nm

200

200

200

200

200

Combined fuel consumption[2]

l/100 km

6.5-6.2

6.6-6.2

(6.7-6.3)

6.9-6.5

7.0-6.6

7.3-7.0

Combined CO2 emissions2

g/km

149-141

150-141

(153-143)

157-149

159-150

168-161

Acceleration 0-100 km/h

s

8.6

7.3 (7.5)

7.1

6.0

6.0

Top speed

km/h

231

246 (240)

241

250

250

And here are the consumption values according to WLTP[3]

 

 

C 180

C 200

C 200 4MATIC

C 300

C 300 4MATIC

Total fuel consumption WLTP

l/100 km

7.2-6.2

7.2-6.3 (7.4-6.5)

7.6-6.6

7.4-6.6

7.9-7.0

Total CO2 emissions WLTP

g/km

163-141

163-143 (168-149)

172-151

169-150

180-160

Overview of Saloon and Estate1 models (diesel engines):

 

 

C 220 d

C 300 d

Displacement

cc

1993

1993

Output

kW/hp

147/200

195/265

at

rpm

4200

4200

Add. output (boost)

kW/hp

15/20

15/20

Peak torque

Nm

440

550

at

rpm

1800-2800

1800-2200

Add. torque (boost)

Nm

200

200

Combined fuel consumption1

l/100 km

5.2-5.0

(5.3-5.0)

5.3-5.0

(5.3-5.1)

Combined CO2 emissions1

g/km

138-131

(140-133)

139-132

(141-134)

Acceleration 0-100 km/h

s

7.3 (7.4)

5.7 (5.8)

Top speed

km/h

245 (242)

250 (250)

And here the consumption figures as per WLTP1[4]

 

 

C 220 d

C 300 d

Total fuel consumption WLTP

l/100 km

5.6-4.9 (5.8-5.1)

5.6-5.0 (5.8-5.1)

Total CO2 emissions WLTP

g/km

148-130 (152-134)

148-131 (152-135)

Plug-in hybrids with an electric range of around 100 kilometres (WLTP)[5][6]

Fourth-generation plug-in hybrids will follow soon after the launch. Electrification is taking a great step forward while using the same base engines. With an electric output of 95 kW (129 hp) and an all-electric range of around 100 kilometres (WLTP), the plug-in hybrid C-Class will operate in all-electric mode in many cases - and on many days without using the combustion engine at all. This is the two-litre variant of the ultra-modern M 254 four-cylinder engine. The complete package is not only very efficient, but also decidedly sporty. Diesel plug-in hybrid Saloon and Estate models will follow.

The new high-voltage system is more compact and more powerful, while the number of high-voltage interfaces has been significantly reduced. The integration of the power electronics into the transmission housing reduces the installation space required, while also simplifying the assembly processes at the production plant. Increasing the system voltage also increases the output, without the need for larger cable cross-sections.

The high energy density of the hybrid traction head is achieved using a permanently excited synchronous motor with internal rotor. The 440 Nm peak torque of the electric motor is available right from the start, resulting in high agility when moving off, along with dynamic driving performance. The full electric power is available up to 140 km/h, at which point it is softly capped.

The high-voltage (HV) battery has been developed in-house by Mercedes-Benz AG. It is part of a fourth-generation family of batteries and represents a logical evolution of the previous generation. It consists of 96 cells in a so-called pouch configuration. The battery has a total capacity of 25.4 kWh, thereby bringing about a significant increase in electrical range to around 100 kilometres. To account for the high energy density, the HV battery has an internal cooling system. The thermal management system can therefore control the operating temperature irrespective of the climate control in the vehicle interior. In addition to continuous operation in hot and cold regions, this also allows quick charging with direct current. Even when the battery is completely discharged, it can be fully charged in around 30 minutes with the optional 55 kW DC charger. A standard-fit 11 kW charger (depending on the market) is available for three-phase charging at a Wallbox connected to the domestic AC mains.

The positioning of the battery in the vehicle brings advantages on a day-to-day basis compared with the previous model: there is no longer a step in the boot, and through-loading is now possible. This improvement is particularly noticeable in the Estate model: the length of the luggage compartment floor has increased by 63 mm to 1043 mm. Tall crates or cases of bottles can be loaded under the cassettes of the retractable luggage cover and dividing net without problems, as the height of the luggage compartment has increased by 150 mm to 732 mm. Compared to the previous model, the luggage capacity has increased by 45 litres to 360 litres, while with the rear seats folded down the Estate model can even accommodate 1375 litres (40 l more). Air suspension and level control at the rear are standard for both the Saloon and Estate models.

The driving experience: considerably more electric

All in all, the driving experience is significantly more electric. In view of the increase in electric range to around 100 kilometres, drivers will be able to cover most everyday journeys under electric power alone. The energy recovery function allows kinetic energy to be recuperated during deceleration or downhill driving, a process that has now also been improved in interaction with the hydraulic brake. The energy recovery output is now over 100 kW. The intelligent, route-based operating strategy activates the electric driving mode where this is most appropriate for the route. It takes into account such factors as navigation data, topography, speed limits and the traffic conditions for the entire planned route. A driver wishing to influence the energy recovery rate can do so directly in three stages controlled by rocker switches behind the steering wheel. This is possible in all driving modes except SPORT. In the driving mode D-, for example, the driver can experience the "one-pedal feeling": When the driver takes his foot off the accelerator the vehicle slows down, purely by electric means, to such an extent that the hydraulic foot brake is often not needed.

The operating strategy communicates with the sensors of the assistance systems and thus efficiently supports the driver in many driving situations. Over longer distances in urban areas, for instance, the car will prioritise electric driving. Two additional driving modes enable the driver to make particularly advantageous use of the plug-in powertrain:

  • BATTERY HOLD: Maintaining the charge state of the high-voltage battery is given priority, e.g. when intending to drive in a city centre or green zone later on; selection of the most suitable drive configuration by the hybrid powertrain system, depending on the driving situation and route.
  • ELECTRIC: Electric driving up to 140 km/h, adjustable energy recovery rate in overrun mode, adaptation of Active Distance Assist DISTRONIC for electric driving, activation of the combustion engine using a pressure point of the accelerator pedal (kick-down)

The plug-in hybrids in the new C-Class have a haptic accelerator pedal module with a pressure point at an accelerator pedal angle of 9.7°. In ELECTRIC mode, this power surge is activated and allows all-electric vehicle operation up to the additional pressure point. If the pressure point is overridden, the combustion engine starts and delivers additional torque. The Power Nap function of ENERGIZING COMFORT is likewise reserved for the plug-in hybrids.

[1] Figures for the Saloon model. Figures for the Estate model, if different, are shown in brackets
[2] The stated figures are the measured "NEDC CO2 figures in conformance with Article 2 No. 1 Implementing Regulation (EU) 2017/1153. The fuel consumption figures were calculated based on these figures. The WLTP figure is relevant for the assessment of the motor vehicle tax.
[3] The stated figures are the measured "WLTP CO2 figures" in accordance with Article 2 No. 3 Implementing Regulation (EU) 2017/1153. The fuel consumption figures were calculated based on these figures.
[4] Figures for the Saloon model. Figures for the Estate model, if different, are shown in brackets
[5] The stated figures are the measured "WLTP CO2 figures" in accordance with Article 2 No. 3 Implementing Regulation (EU) 2017/1153. The fuel consumption figures were calculated based on these figures. Power consumption and range were determined on the basis of Commission Regulation (EU) No. 2017/1151.
[6]  All figures shown are provisional. The vehicle is not on sale yet.

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