22/5/11

Overview: Mercedes-Benz E-class drivetrains

Mercedes has revised the drivetrains of its E-class cars with the aim of improving efficiency.

There are two new petrol engines, in the form of the Blue Direct V6 and V8 units. All petrol and diesel engines in the E-class are now directly fuelled, and a stop-start system is now standard on all derivatives. As we have come to expect with Mercedes, the stop-start system — when it is fitted to cars with an automatic transmission — does not work if the driver holds the car on the parking-brake: the engine is shut off only if the car is held using the foot-brake, which is not a safe practice for any but the briefest pause. In manual transmission cars, the stop-start system shuts the engine off whenever the engine is in neutral with the clutch pedal released.

Mercedes’ 7G-Tronic Plus seven-speed automatic transmission has been revised, and is now also available on four-cylinder models.

Petrol engines

Updating the powertrain has led to improved fuel efficiency across the board. The 184PS E 200 Blue Efficiency with the 7G-Tronic Plus gearbox now returns fuel consumption figures between 6.5l/100km and 6.9l/100km over the NEDC cycle. This equates to 40.9mpg-43.4mpg or 152g/km-160g/km CO₂. The figures for the E 200 with the six-speed manual transmission are markedly worse: 7.1l/100km-7.4l/100km (38.1mpg-39.7mpg; 169g/km-176g/km CO₂).

The E 250 Blue Efficiency is the more powerful of the two four-cylinder petrol models on offer. Delivering 204PS — the same headline figure as the E 250 CDI — its NEDC fuel consumption returns show a 13 per cent. saving over the previous model: 6.6l/100 km-7.0l/100 km, equivalent to 40.3mpg-42.8mpg and 154-162g/km CO₂.

Two V-engines are available — a V6 and a V8. These are members of Mercedes’ new V-engine family that débuted in the current S-class and CLS model. They feature the third incarnation of Mercedes’ Blue Direct injection, with injection pressures of 200 bar (20MPa) along with spray-guided stratified charge combustion. Piezo injectors allow up to five injections per power stroke.

Stratified combustion is extended with a newly-developed lean-burn process known as ‘homogeneous stratified’, which greatly widens the characteristic map for lean-burn combustion in the V6 engine. The first fuel spray is injected on the intake stroke, whereupon a homogeneous basic mixture is formed; the stratified injection takes place on the compression stroke prior to ignition, is controlled according to the engine management map and takes the form of a single or double injection.

A multi-spark ignition (MSI) system enables up to four sparks to be triggered in rapid succession within one millisecond.

The E 350 Blue Efficiency is powered by an atmospheric V6, distinguished from its predecessor not least by the change in the block’s V angle from an odd (for a V6) 90 degrees to a conventional 60°. The old engine used a balancer shaft to compensate for primary vibrations caused by the block angle; the new V6 doesn’t need a balancer shaft and doesn’t have one.

A completely new air intake system with a variable-resonance intake manifold is deployed.

With the same swept volume, the headline output of the E 350’s 3.5 V6 has increased from 292PS to 306PS, and from 365Nm to 370Nm. Along with the revised transmission and the standard stop-start system, the new engine has delivered a 20 per cent. fuel saving over the NEDC compared to the preceding model, though peak output has increased by 14PS to 306PS. This new V6 returns overall consumption figures of 6.8-7.0l/100km (40.3mpg-41.5mpg) depending on tyre equipment, down from 8.5l/100km (33.2mpg). These figures correspond to CO₂ emissions of 159-164g/km. Mercedes claims that the new E 350 will reach 100km/h from a standing start in 6.3s; maximum speed is limited to 155mph.

With the new V8 E 500 Blue Efficiency, it would be hard to claim that efficiency equals outright economy. Nevertheless, the model has undoubtedly taken a big step forward, with a 17 per cent. improvement in fuel consumption on the rolling road. And despite losing 828cc, outputs are substantially up in comparison with the previous model: the twin-turbocharged V8 delivers 408PS (previously 388PS) and 600Nm (530Nm). At the same time, fuel consumption has fallen from 10.8l/100km (26.1mpg) to 8.9l/100km (31.7mpg) over the NEDC test cycle. Standing start acceleration to 100km/h is achieved in a claimed 5.2s; maximum speed is limited to 155mph.

The petrol engines’ efficiency improvements is partly a result of the standard fitment of a start-stop system. This is standard on diesel models as well. Improvements to the 7G-Tronic Plus gearbox also help: this transmission is standard on E 250, E 350 and E 500 models. The unit has a new torque converter with reduced slip, an ‘Eco’ shift program, revised ratios, and an auxiliary oil pump to maintain operating pressure during automatic stops of the power-unit. Low-friction components and low-viscosity lubricant help to reduce the operating pressure.

Diesel engines

Improvements in efficiency, largely down to the transmission improvements and stop-start system we have already mentioned, are most marked with four-cylinder models. Engine oil pressure control and belt drives have been tweaked, while turbochargers are also revised.

The E 220 CDI Blue Efficiency delivers 170PS, while the E 250 CDI Blue Efficiency offers 204PS. Overall fuel consumption over the NEDC rolling-road cycle with the standard six-speed manual transmission is between 5.0l/100km and 5.3l/100km (53.3mpg and 56.5mpg) depending on wheel and tyre equipment for both engines, with CO₂ outputs between 130g/km and 139g/km. In the automatic versions, consumption figures have fallen by 16 per cent. to between 4.9l/100km and 5.3l/100km (53.3mpg and 57.6mpg), again for both the E220 CDI and E 250 CDI; CO₂ figures are 129-138g/km.

Both the six-speed manual and 7G-Tronic variants of the 136PS E 200 CDI Blue Efficiency entry-level diesel now have a combined NEDC fuel consumption of between 5.1l/100km and 5.4l/100km (52.3mpg-55.3mpg; 134-141g/km CO₂).

The all-wheel drive E 250 CDI 4Matic Blue Efficiency, which is available only with the 7G-Tronic automatic transmission, also benefits from the changes made to the rear-driven version.

Natural gas power: E 200 NGT Blue Efficiency

The E 200 NGT Blue Efficiency runs on CNG or petrol: it is what Mercedes describes as ‘bivalent’ — clearly not in the chemical sense, but simply meaning that it will run on two fuels. Its 1796cc four-cylinder engine offers 163PS and 240Nm. Its four-cylinder engine can be operated on both premium petrol and natural gas. In addition to the petrol tank, three natural gas tanks are fitted: one behind the rear seat backrest and two under the boot floor. They have a combined capacity of 121.5l or 19.5kg. In natural gas operation, the combined NEDC fuel consumption of the E 200 NGT is 5.5kg/100km: this corresponds to CO₂ emissions of 149g/km. In petrol mode the combined consumption is 8.1l/100km.

The NGT’s operating range in natural gas mode is around 220 miles. If you run out of gas, the car automatically switches to petrol operation, increasing the range to over 600 miles. The engine management system allows a smooth changeover from petrol to gas and vice versa at any time.

As part of the standard Blue Efficiency package, the energy consumption of major ancillary units has been cut in all E-class petrol and diesel models.

A demand-controlled oil pump is used, operating with two pressure stages. At low engine speeds and loads, the pump operates at a low pressure. The high pressure level is only activated at high loads and engine speeds. Especially in urban traffic, this means that the lubrication and cooling points of the engine can be supplied for a lower energy input.

The demand-controlled coolant pump is only activated when the best possible operating temperature has been reached, thereby achieving a faster warm-up. There is also energy-saving control of the fuel pump, air conditioning compressor and power steering.

‘Intelligent’ alternator management is used, taking the unit off-load when the engine is under load and when the battery is fully charged, with charging taking place only on the overrun.