Engine and drive system - Efficiency and fun at the wheel: yesterday's utopia is today's reality

Mar 13, 2014

Powerful and efficient petrol and diesel engines, all equipped with the ECO start/stop function and complying with the Euro 6 emissions standard, provide for lively performance and great fun at the wheel. At the same time they lower fuel consumption and CO2 emissions by up to 20 percent compared with the predecessor thanks to high energy efficiency.

An innovation is a small diesel engine with a displacement of 1.6 litres (OM 626). Reduced weight, compact design and low specific fuel consumption are among its special merits. Depending on its configuration, the single-stage turbocharged four-cylinder engine generates 85 or 100 kW (115 or 136 hp) of power from a displacement of 1598 cc and delivers 280 or 320 Nm of torque. This engine places the new C-Class in a leading position within its segment in terms of CO2 emissions.

Technical data of the OM 626

Cylinder arrangement/number

4/in-line

Displacement cc

1598

Bore mm

80

Stroke mm

79.5

Valves per cylinder

4

Cylinder spacing mm

88

Compression ratio  

15.4:1

Rated power (kW at rpm)

100 at 3800

Rated torque (Nm at rpm)

320 at 2000

The OM 626 is the first passenger car diesel engine to use steel pistons. Thanks to reduced friction and better thermal behaviour they offer clear advantages in terms of fuel consumption over aluminium pistons, which are state of the art today. The crankcase of the new diesel engine, which is characterised by particularly comfortable NVH properties, is made of cast iron, the cylinder head of an aluminium alloy. An overhead camshaft actuates two intake and two exhaust valves per cylinder.

The turbocharger with variable turbine geometry has a turbine rotor with a diameter of 37.5 millimetres and an impeller with a diameter of 45 millimetres. A vacuum unit controlled by the engine management system via an electropneumatic vacuum converter adjusts the particularly aerodynamic "S design" vanes. The compact design of the turbine housing results in low heat and flow losses in the exhaust stream. This creates favourable conditions for a high boost ratio and good exhaust-gas conversion.

The common-rail direct injection system of the new small diesel engine operates at a maximum injection pressure of 1600 bar. Solenoid injectors with flow-optimised hole geometry ensure low emissions and quiet operation.

The new diesel engine is the product of the strategic cooperation with Renault. It is produced by Renault and assembled in part in Bremen. Technology modules specific to Mercedes-Benz make the engine more efficient. They include the ECO start/stop function, the ancillaries and a special dual-mass flywheel that better compensates imbalances and makes a balancer shaft unnecessary. The engine control unit with additional functions ensures a driveability that can be rightfully expected from a Mercedes.

Environment-friendly and powerful – the BlueTEC diesel engines

In addition to the new small diesel engine, an advanced version of the 2.2-litre four-cylinder diesel engine is also available in several output variants. The diesel engines will thus cover an output range from 85 kW (115 hp) to 150 kW (204 hp). The C 220 BlueTEC will also be optionally available with an output of 120 kW (163 hp) as the BlueEFFICIENCY Edition.

All diesel engines of the new C-Class are equipped with the established SCR technology (selective catalytic reduction) for particularly environment-friendly driving and ensure that the C-Class models with diesel engines attain at least efficiency class A, and in most cases even efficiency class A+. The models with 4MATIC four-wheel drive are the exceptions.

Diesel engines in the top efficiency class

Model

Displace-ment

cc

kW/hp

Nm

0-100 km/h

in sec.

l/100 km

CO2

g/km

Efficiency class

C 180 BlueTEC

1598

85/116

280

-

3.8*

99*

A+

C 200 BlueTEC

1598

100/136

300

-

3.8*

99*

A+

C 220 BlueTEC

2143

125/170

400

7.7

4.0

103

A+

C 220 BlueTEC ECO

2143

120/163

400

7.4

4.2

107

A+

C 250 BlueTEC

2143

150 (204)

500

6.6

4.3

109

A+

C 300 BlueTEC HYBRID

2143

150 + 20/ 204+27

500 + 260

-

3.6

94

A+

*provisional figures

Hybrid with four-cylinder diesel engine

In addition, Mercedes-Benz offers a diesel engine combined with a hybrid module. The C 300 BlueTEC HYBRID with four-cylinder diesel engine and compact electric motor generates a power output 150 + 20 kW (204 + 27 hp) and runs on only 3.6 litres of diesel per 100 km/h in NEDC combined mode (provisional figure).

In addition to the combustion engine and the electric motor the hybrid module of the C 300 BlueTEC includes the 7G-TRONIC PLUS transmission, combined power electronics with DC/DC converter and a high-voltage lithium-ion battery. The latter is located next to the fuel reservoir, has a high energy density and is consequently particularly suited as a storage medium for the electric energy generated by the electric motor. An additional conventional 12-volt battery is installed in the multifunction recess in the rear of the hybrid model. It powers all standard consumers and the high-voltage components.

The hybrid model is furthermore equipped with an electric vacuum pump and a braking system for effective energy recuperation custom-developed for the hybrid. An electric refrigerant compressor ensures the automatic climate control system also works when the combustion engine is switched off. This technology makes pre-entry climate control of the vehicle possible to ensure pleasant interior temperatures already when getting into the vehicle.

Thanks to the particularly compact components, the hybrid technology could be fitted in the standard installation spaces without restricting the boot volume.

Hybrid technology unlocks new possibilities

The hybrid model offers all traits of a modern hybrid vehicle. These include first and foremost:

  • Silent start – the electric motor moves the vehicle quietly for the first few metres.
  • Electric driving - a limited distance can be covered in all-electric mode at speeds up to about 35 km/h; this is useful for manoeuvring and in stop-and-go traffic, for example.
  • Sailing – the vehicle drives with the engine switched off when coasting or on slight downhill gradients. If the driver releases the accelerator at speeds below 160 km/h, the combustion engine is decoupled and switched off - the vehicle enters sailing mode. In the process the electric motor generates overrun torque so that the vehicle coasts and decelerates like a conventional vehicle. The recuperated energy is stored in the high-voltage battery and is available for boosts and electric driving.
  • Sailing PLUS – this function is activated in sailing mode with the right-hand steering-wheel shift paddle. It reduces energy recuperation to a minimum. While the combustion engine remains switched off, only a small amount of the kinetic energy is used for recuperation. Instead it provides a higher coasting speed and/or longer coasting distance – an advantage on longer downhill stretches and in approaching traffic lights and junctions with foresight.
  • Boost effects - the electric motor boosts the combustion engine with its powerful torque. This enables faster overtaking and acceleration manoeuvres as well as more tangible agility and consequently more safety and fun at the wheel.
  • Recuperation - while on the move, as soon as the driver releases the accelerator, overrun recuperation begins. This converts the vehicle's kinetic energy into electrical energy and stores it in the high-voltage battery. Energy is also converted via the electric motor when decelerating using the service brake.

The electric motor provides yet another benefit: it dampens vibrations in the powertrain and consequently increases ride comfort.

A further particularly economical hybrid model which is to follow at a later juncture will feature state-of-the-art plug-in technology.

The petrol engines: powerful, fast and clean

Four-cylinder petrol engines with power outputs ranging from 115 to 180 kW (156 to 245 hp) will also be available. They include the special C 180 ECO Edition model, which as the BlueEFFICIENCY Edition qualifies for efficiency class A. A six-cylinder petrol engine rated at 245 kW (333 hp) will follow in due course.

The BlueDIRECT four-cylinder petrol engines of the C-Class combine spontaneous response and exemplary power delivery with high efficiency and best-in-class emissions. To this end, Mercedes-Benz has transferred the BlueDIRECT technology from the V6 and V8 engines to the four-cylinder engine. The Mercedes engineers have developed the third generation of the direct injection system with spray-guided combustion, which was first offered in the series production of passenger cars by Mercedes-Benz. The system pressure is up to 200 bar, the pressure being variably optimised according to the engine's mapping. Piezo injectors enable optimal mixture formation with up to five injections per power stroke.

The third-generation direct injection system also features "rapid multi-spark ignition" (MSI). Following the first spark discharge and a brief combustion period, the coil is quickly recharged and a further spark is discharged. The MSI system enables up to four sparks to be discharged in succession within one millisecond, creating a plasma with a larger spatial expansion than conventional ignition.

The rapid multi-spark ignition can be controlled to vary both the timing of the sparks and the combustion period to suit the relevant operating point. This provides scope for optimising the centre of combustion and improved residual gas compatibility. This in turn reduces fuel consumption. The result of this is excellent utilisation of the fuel with minimum emissions.

The thermal management is also efficient: when the engine is cold, no coolant runs through the engine thanks to an on-demand water pump with flow-optimised ball valve. As a result, the combustion chambers heat up more quickly after starting up the engine. The thermostat is electronically controlled and the coolant temperatures are adjusted according to driving style and ambient conditions. The thermostat itself is also a flow-optimised ball valve. In the interest of high efficiency, the volumetric flow of the oil pump is likewise controlled as in the V engines.

All engine variants are designed for operation with E10 premium petrol and an octane rating of 95 RON.

The powerful petrol engines

Model

Displacement

cc

kW/hp

 

Nm

0-100 km/h

in sec.

l/100 km

CO2

g/km

Efficiency class

C 180

1595

115/156

250

8.2

5.0

116

A

C 200

1991

135/184

300

7.5

5.3

123

B

C 250

1991

155/211

350

6.6

5.3

123

B

C 400 4MATIC

2996

245/333

480

-

less than 8.0*

-

D

* provisional figure

ECO start/stop function with direct starting as standard

The ECO start/stop function included as standard in all models operates with starter motor-supported direct starting. This means: when the engine is switched off, the angle of the crankshaft is registered by a new crankshaft sensor so that the engine control unit knows the positions of the individual cylinders. On restarting, it can then select the cylinder that is in the most suitable position for first ignition. After the starter has briefly turned over the engine, reliable injection, ignition and combustion is immediately possible in the ideally positioned cylinder.

Optimised powertrain for more comfort and efficiency

For the four-cylinder engines of the new C-Class Mercedes-Benz offers two new 6-speed manual transmissions tailored to the respective engine variant (diesel or petrol). Both stand apart first and foremost by virtue of their enhanced ease of shifting coupled with increased shifting precision and a harmonious gear change sequence. Dry sump lubrication and improved low-friction oil enable comfortable gearshifts even after a cold start.

Smooth automatic gearshifts are provided by the 7G-TRONIC PLUS automatic transmission with DIRECT SELECT selector lever and DIRECT SELECT shift paddles, which has undergone further development at Mercedes-Benz in the interests of enhanced environment-friendliness and fun at the wheel.

Among the traits of the latest evolutionary stage of the 7G-TRONIC PLUS are the new torque converter with reduced slip, an ECO transmission mode with improved gear spread as well as an auxiliary oil pump that maintains the operating pressure when the engine is automatically switched off. Friction-optimised components in conjunction with low-friction oil make it possible to lower the operating pressure.

A new feature is short-term M mode. The benefit here is that if the driver has shifted up or down manually, the transmission independently switches back to the fuel-efficient, automatic shift mode after a set period of time. This period of time is extended under specific conditions (no accelerator pedal use, e.g. on downhill gradients, high lateral acceleration, e.g. when cornering, or if the speed falls below a minimum threshold when coming to a stop), preventing the return to automatic mode.

In short-term M mode as well as in "fixed" M mode, the driver receives gear change recommendations in the multifunction display of the instrument cluster, to enable an efficient driving style.

4MATIC all-wheel drive

Traction and driving stability can also be improved in the C-Class with the 4MATIC permanent all-wheel drive system - particularly in difficult road conditions. As ever, the combination of the ESP® drive dynamics control system with the 4ETS electronic traction system makes regular differential locks superfluous. This saves weight and noticeably improves safe handling as well as ride comfort. The transfer case of the all-wheel drive system is integrated into the main transmission.

The all-wheel drive models impress with:

  • good traction characteristics, with a 45:55 power split between the front and rear axle
  • low fuel consumption due to the improved efficiency of the drivetrain
  • good noise and vibration characteristics
  • additional weight of just 70 kg, compared with additional weight of up to 120 kg for the competition
  • unchanged body shell as well as unrestricted interior and luggage compartment space due to the compact design
Mercedes-Benz C-Class: Free-standing central display
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Mercedes-Benz C-Class: High-voltage cable of the C 300 BlueTEC HYBRID
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Mercedes-Benz C-Class: Electric motor of the C 300 BlueTEC HYBRID
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Mercedes-Benz C-Class: C 180, Output graph (german version)
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Mercedes-Benz C-Class: C 200, Output graph (german version)
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Mercedes-Benz C-Class: C 220 BlueTEC, Output graph (german version)
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Mercedes-Benz C-Class: Mercedes Benz Motor OM651, four cylinder diesel engine
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Mercedes-Benz C-Class: Mercedes Benz Motor M274, four cylinder petrol engine
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