The new Mercedes-Benz E-Class Coupé - PART IX


Stuttgart, Germany, Apr 22, 2009

Drive system: Turbo, piezo and direct injection - New engines which offer big fuel savings

Petrol engines: new four- and six-cylinder models with direct injection
Diesel: four-cylinder model with two-stage turbocharger
Transmissions: technology for fuel-efficient motoring

With its newly developed direct-injection diesel and petrol engines, Mercedes-Benz has taken further major strides forward in its quest to reduce both fuel consumption and exhaust emissions - without compromising on agility and driving enjoyment.

The new four-cylinder diesel engine in the E 250 CDI BlueEFFICIENCY Coupé, for example, shows just how much progress has been made: with an output of 150 kW/204 hp, a peak torque of 500 Nm and a displacement of 2.2 litres, it develops around 36 percent more power and delivers 47 percent more torque than the previous four-cylinder diesel engine yet consumes around 17 percent less fuel: 5.1 litres per 100 kilometres (provisional NEDC combined figure). What's more, CO2 emissions are just 135 grams per kilometre. All of which means that the new CDI Coupé is more fuel-efficient than comparable models in this output category.

In the case of the petrol models too, "more power and more driving pleasure with even lower fuel consumption" proves to be the perfect formula: the likewise new E 250 CGI BlueEFFICIENCY Coupé model with direct petrol injection has a displacement of 1.8 litres and an output of 150 kW/204 hp yet consumes a mere 7.2 litres of premium unleaded petrol per 100 kilometres (provisional NEDC combined figure) - around one litre per 100 kilometres (12 percent) less than the previous four-cylinder engine (135 kW/184 hp) with conventional fuel injection and a supercharger. The CO2 emissions of the direct-injection model have been cut to 167 grams per kilometre.

As with carbon dioxide emissions, the engines for the new E-Class have also taken a further major step towards the future when it comes to exhaust gas emissions: all of the powerplants meet the requirements of the EU 5 standard, whose limits are up to 80 percent more stringent than those specified by previous standards.

Diesel engines: new four-cylinder unit featuring state-of-the-art common-rail technology

As well as being economical and ecofriendly, the four-cylinder CDI engine impresses with its exceptional agility, effortlessly superior power delivery and exemplary refinement. The former is reflected in the performance figures: the new E 250 CDI BlueEFFICIENCY Coupé needs 7.4 seconds to accelerate from 0 to 100 km/h.

The engine is part of a new series of four-cylinder powerplants, which sees Mercedes-Benz introducing the fourth generation of its tried-and-trusted common-rail direct-injection units into series production. One of its hallmarks is a 400-bar increase in the maximum rail pressure, which now stands at 2000 bar. This increased pressure potential was a key factor in raising the engine output to up to 150 kW/204 hp and the peak torque to 500 Nm whilst also achieving a significant reduction in untreated emissions.

Newly developed piezo injectors are key components in the latest CDI engine generation. They use their piezoceramic properties to change their crystal structure - and therefore their thickness - in a matter of nanoseconds when electrical voltage is applied. The new injectors are equipped with a stack of thin piezo-ceramic layers (called the "piezo stack") to enable them to achieve a sufficient overall lift from the very small lift per layer.

In contrast to the systems commonly used to date, this lift activates the nozzle needle directly, so that the fuel injection can be adjusted even more precisely in line with the current load and engine-speed situation - for example by means of precise multiple injections, which have a favourable effect on emissions, fuel consumption and combustion noise. What's more, the engine is far quieter when idling than its predecessor.

Another key factor behind the impressive output and fuel consumption at full load with respect to emissions is the maximum ignition pressure. And, with 200 bar, the new four-cylinder diesel unit from Mercedes-Benz is among the leading contenders in the field of passenger-car diesel engines.

Torque: two-stage turbocharging for exceptional pulling power

The new diesel engine in the E 250 CDIBlueEFFICIENCY Coupé model marks the debut of two-stage turbocharging in a series-production diesel engine for Mercedes-Benz passenger cars. The aim is to achieve further advantages compared to a single-stage turbocharger, for example a further improvement in start-up performance and peak output.

The compact module for the new two-stage turbocharger consists of a small high-pressure (HP) turbocharger and a large low-pressure (LP) turbocharger. These are connected in series, and each has a turbine and a compressor driven by this turbine. The HP turbine is located directly at the exhaust manifold and initially allows exhaust gas to flow through it; it then rotates at up to 215,000 revolutions per minute. The HP turbine housing features an integral bypass duct, which can be opened or closed by means of a charge-pressure control flap triggered by a vacuum cell. If the flap is closed, the whole exhaust stream flows through the HP turbine, meaning that the exhaust-gas energy is available solely for the HP turbine drive.

This means that the optimum charge pressure can be built up at low engine revs.
As the engine speed increases, the charge-pressure control flap opens. Any remaining exhaust gas energy drives the HP turbine at a maximum speed of up to 185,000 revolutions per minute. To protect against overloading, the LP turbine is also equipped with a bypass, which is opened or closed by means of a wastegate. Once the engine reaches medium revs, the HP turbine's charge-pressure control flap is opened so wide that the HP turbine ceases to perform any appreciable work. This allows the full exhaust gas energy to be directed with low losses into the LP turbine, which then does all of the turbine work.

The two compressors are likewise connected in series and are in addition connected to a bypass duct. The combustion air from the air cleaner first flows through the low-pressure compressor, where it is compressed as a function of the LP turbine's operating energy input. This pre-compressed air then passes into the high-pressure compressor, which is coupled to the HP turbine, where it undergoes further compression. The result is a genuine two-stage turbocharging process.

The key benefit of this sophisticated, on-demand control of the combustion air supply by means of two turbochargers is the improved cylinder charging and, consequently, a high torque even at low revs. What's more, fuel consumption is reduced. During normal operation, the advantages of this concept can be seen in the harmoni­ous driving characteristics without turbo lag, a good torque curve across the entire engine speed range, spontaneous throttle response and notice-ably improved performance.

As a logical addition to the turbocharger system, Mercedes-Benz installs a larger intercooler than the one seen in the previous models, which reduces the temperature of the compressed and heated air by up to 140 degrees Kelvin so that a larger volume of air can enter the combustion chambers.

Cooled exhaust gas recirculation to reduce NOx emissions

The newly developed EGRvalve works like a rotary disc valve and ensures precise control of the fresh air and recirculated exhaust gas. So as to optimise the quantity of exhaust gas recirculated and thereby achieve high recirculation rates, the exhaust gases are cooled down as required in a highly efficient heat exchanger with a large cross-sectional area. Together with the HFM (hot-film air-mass sensor) module integrated in the fresh-air ducting, which provides the engine control unit with precise information about the current fresh-air mass, this setup brings about a significant reduction in nitrogen oxide emissions.

The combustion air subsequently flows into the charge-air distributor module, which supplies air to each cylinder in a uniform manner. Built into the distributor module is an electrically controlled intake port shutoff, which allows the cross-sectional area of each cylinder's intake port to be smoothly reduced in size. This alters the swirl of the combustion air in such a way as to ensure that the charge movement in the cylinders is set for optimum combustion and exhaust emissions over the full spectrum of engine loads and speeds.

Pedestrian protection: the advantages of a rear-mounted camshaft drive

Another of the highlights of the new four-cylinder diesel engine is the rear-mounted camshaft drive, which allows statutory pedestrian protection requirements to be met when the engine is installed longitudinally and the bonnet rises from front to rear. The valve timing mechanism is another new development and reduces friction at the 16 intake and exhaust valves, which are controlled by one overhead intake camshaft and one overhead exhaust camshaft acting via cam followers featuring hydraulic valve clearance compensation. The camshaft, Lanchester balancer and the ancillary assemblies are driven by a combination of gearwheels and just a short chain drive.

Six-cylinder CDI: increased output and fuel consumption of 6.8 litres per 100 kilometres

The V6 diesel engine for the E 350 CDI BlueEFFICIENCY Coupé is one of the most sophisticated compression-ignition units on the world market. It offers greater output, comfort and driving enjoyment than other engines thanks to the immense torque of 540 Nm alone - compared to the 510 Nm developed by the previous model - which is available between 1600 and 2400 rpm, ensuring outstanding agility when accelerating from rest and exemplary flexibility when accelerating in any gear: the vehicle accelerates from 0 to 100 km/h in 6.7 seconds. The six-cylinder unit now has an output of 170 kW/231 hp instead of 165 kW/224 hp as before.

Despite the higher output and torque, fuel consumption is considerably less than that of the previous model, amounting to just 6.8 litres per 100 kilometres, equivalent to 179 grams of CO2 per kilometre. The 7G-TRONIC seven-speed automatic transmission is specified as standard for the E 350 CDI BlueEFFICIENCY Coupé.

The Mercedes engineers have gone to great lengths to optimise the technology at the heart of the V6 diesel engine, reducing the compression from 17.7 to 15.5 and enhancing the turbocharger with a more efficient EGR cooling zone, switchable bypass duct, ceramic glow system, modified injection nozzles and optimised air ducting.

The range of diesel engines for the new E-Class at a glance:

Petrol engines: new four-cylinder unit with direct injection

CGIappears at the end of the model designation of the four- and six-cylinder petrol engines for the new E-Class Coupé, signifying that Mercedes-Benz uses
direct petrol injection for all of these powerplants - a technology which allows further advances when it comes to reducing petrol consumption.

Compared to conventional port injection, direct fuel injection allows higher compression and, therefore, improved thermodynamic efficiency, saving motorists money at the pump: the new four-cylinder direct-injection powerplant consumes up to 13 percent less fuel than the previously installed supercharged engine with port injection. Power and torque, however, are much higher than in the case of the outgoing model: 150 kW/204 hp instead of 135 kW/184 hp and 310 Nm instead of 250 Nm. Hence the new CGI Coupé also boasts even more impressive performance figures:

0 to 100 km/h: 7.4 seconds instead of 9.1 seconds as before

Mercedes-Benz equips the E 250 CGI BlueEFFICIENCY Coupé with a five-speed automatic transmission.

The four-cylinder engine is made almost entirely of aluminium: the crankcase is made of diecast aluminium, while a special, high-strength aluminium alloy is used for the cylinder head. Two forged overhead camshafts with variable adjustment are used to control the 16 valves. A vane-type adjuster with integrated control valve allows fast and smooth adjustment of the timing, ensuring that it is always at the optimum setting. This setup has two advantages: firstly, the variable camshaft adjustment enables a high torque yield even at low revs; secondly, this technology allows high specific outputs. The valves are controlled by means of cam followers and feature maintenance-free, hydraulic valve clearance compensation.

Thermal management: coolant circulation based on engine temperature

The Mercedes engineers have paid special attention to the engine's warm-up
governor because also has a major effect on fuel consumption. This is why the new direct-injection petrol model features an electronically controlled thermostat to ensure that circulation of the coolant is stopped when the engine is cold. This setup allows the engine oil to heat up quickly and, therefore, minimises in-engine friction. This intelligent thermal management system is logic-controlled. In other words, it is based on driving style, ambient temperatures and other parameters.

The turbocharger module, welded to the exhaust manifold on the engine's exhaust side, features a wastegate valve and a deceleration air function for controlling the pressure characteristics. There were very good reasons for using a turbocharger in place of the previously installed mechanical supercharger - not least the higher efficiency as the engine does not need to provide the extra drive power required for the mechanical supercharger. What's more, the turbocharger takes up far less space than the supercharger, is around four kilograms lighter and, in addition, offers better noise and vibration characteristics. The Mercedes engineers brought about a noticeable improvement in the turbocharger's bottom-end response by incorporating newly developed turbine geometry and a cylinder-flushing process.

Direct injection: pressure of up to 140 bar and new multi-hole injectors

In the direct-injection system, the air and fuel are not mixed until they reach the combustion chambers. With the help of an injector, the fuel is injected into the cylinders at an angle of 30 degrees and, depending on the engine operating characteristics, at a pressure of up to 140 bar. Here the fuel droplets and the air particles form a mixture which is guided to the spark plugs via specially shaped recesses in the pistons. By way of comparison, the fuel pressure in a four-cylinder engine incorporating conventional injection technology is approximately 3.8 bar.

In order to ensure optimum swirl in the mixture, thus making combustion fast and as complete as possible, the CGI engine has intake ports with specially calculated flow characteristics. An adjustable swirl flap is also used so as to produce high turbulence in certain operating ranges and thus improve the combustion process. The high-pressure fuel pump is driven by the intake camshaft, while a quantity control valve integrated in the pump module ensures on-demand metering of the fuel supply. A pressure regulator with its own sensor, monitored by the engine control unit, controls the pressure in the fuel line (rail), which is directly connected to the multi-hole solenoid injectors. The four-cylinder direct-injection units operate in a homogeneous range, in other words with a stoichiometric air-to-fuel ratio of 14.7 : 1 (Lambda = 1), which is important for emission control by means of three-way catalytic converter. The new four-cylinder direct-injection engines meet the requirements of the EU 5 emission standard.

Comfort-enhancing measure: balancer in the crankcase

In addition to exemplary power delivery, low fuel consumption and low exhaust emissions, the new Mercedes four-cylinder engines have a further advantage, namely outstanding refinement, thanks in no small part to the newly developed Lanchester balancer: two forged shafts supported in three bearings, which are arranged below the crank mechanism and counter-rotate at twice the crankshaft speed. In so doing, they compensate for the inertia forces that are caused by the motion of the pistons, for example, which can lead to irritating vibrations. The aluminium housing that contains the bearing-mounted balancer shafts is located in the oil sump, where it is bolted to the crankcase from below. The crankcase also contains the controlled engine oil pump, which is driven by one of the two shafts by means of a gear pair.

Six-cylinder engine: CGItechnology with spray-guided direct petrol injection

The new E 350 CGI BlueEFFICIENCY Coupé is powered by the world's first petrol engine with spray-guided direct injection. The six-cylinder powerplant develops 215 kW/292 hp and provides a peak torque of 365 Nm from 3000 rpm. Thanks to the state-of-the-art engine technology, which Mercedes-Benz has modified right down to the last detail, fuel consumption is reduced to 8.5 litres per 100 kilo-metres (NEDC combined figure), which is 14 percent lower than the figure for the previous model, whose V6 engine featured port injection. These exemplary performance and fuel-consumption figures are achieved using cost-efficient premium unleaded petrol (RON 95). The seven-speed automatic transmission is fitted as standard.

What's more, the highly economical and environmentally compatible CGIpowerplant provides a unique driving experience: it takes the V6 Coupé just 6.5 seconds to accelerate from 0 to 100 km/h.

Mode of operation: stratified-charge mode, even at higher engine speeds

Mercedes-Benz was the first car manufacturer to introduce spray-guided direct petrol injection into series production in 2006. Thanks to higher thermodynamic efficiency, this technology allows better use of the fuel and, therefore, lower fuel consumption and lower exhaust gas emissions. The key benefit of the six-cylinder engine is delivered in stratified-charge mode, when the powerplant operates with a high degree of excess air and, therefore, extremely fuel-efficiently. This advantageous "lean-burn operation" is now also possible when the Mercedes direct-injection unit is running in higher engine-speed and load ranges because the combustion chambers are supplied with fuel several times in succession within a fraction of a second in every combustion cycle, thus vastly improving mixture formation, combustion and consumption.

Fast and highly precise piezo injectors are among the key components of the second-generation direct petrol injection system. They open their nozzle points outwards, forming an annular gap that is mere micrometres in size, shaping the jet of fuel and ensuring its even, hollow-cone-shaped dispersion. Thanks to their ability to switch within milliseconds, the piezo injectors also allow the multiple injection that is also of benefit for lean-burn operation, thus playing a crucial role in achieving the engine's exemplary consumption figures. A high-pressure pump with downstream distributor and pressure valve supplies the fuel and ensures on-demand flow control. With a level of up to 200 bar, the system's fuel pressure is several times higher than that in a conventional port injection system.

The combustion process with several injections in succession per combustion cycle developed by Mercedes-Benz also enhances the refinement and emission characteristics of the V6 engine. Tests show that untreated emissions (hydrocarbons) are reduced by more than half in the warm-up phase. Plus the specifically targeted injection and combustion control allows higher temperatures in the exhaust manifold, ensuring faster heating of the catalytic converters.

Emissions are controlled by two close-coupled three-way catalytic converters with linear lambda control, which are activated immediately after a cold start. Mercedes-Benz reduces nitrogen-oxide emissions by means of two-pipe electrically controlled exhaust gas recirculation, which directs up to 40 percent of the exhaust gases back into the cylinders, depending on the engine's operation, and by means of two NOx storage catalytic converterson the underbody. During lean-burn operation, these catalytic converters absorb the nitrogen oxides and re-release them in short regeneration phases so that they react chemically to form harmless nitrogen.

Four valves per cylinder, variable intake and exhaust camshaft adjustment, a two-stage intake manifold, a balancer shaft and intelligent thermal management with a logic-controlled thermostat are further technical highlights of the V6 engine with direct injection. The crankcase and cylinder head are made of aluminium; the cylinders are equipped with liners that have a lightweight, low-friction aluminium-silicon coating that is stable in shape.

Precision-modified eight-cylinder engine

The eight-cylinder unit in the E 500 Coupé - the flagship powerplant in the new generation of Mercedes-Benz V engines - provides a blend of high output and torque yield with exemplary refinement and effortlessly superior agility. The extent of the powerplant's capability is highlighted by the performance figures for the new top-of-the-range E-Class Coupé, which is equipped with the 7G-TRONIC 7-speed automatic transmission as standard:

0 to 100 km/h: 5.2 seconds

Mercedes engineers use an intelligent valve-timing concept, achieving a level of progress that is a major factor behind the excellent torque and output characteristics. An optimum supply of fresh mixture for the cylinders is assured thanks to four-valve technology and, above all, continuously variable and continuous intake and exhaust camshaft adjustment. The valves are always opened at precisely the right moment in any driving situation, significantly improving the gas cycle in the combustion chambers and reducing energy losses.

The "quadruple" continuously variable camshaft adjustment process is further enhanced by shifting camshafts, which are used to enable opening of the exhaust valves and, therefore, further improve the engine's gas cycle. The exhaust cams are designed so that the valves open at different times during the exhaust process, depending on the firing order. As a consequence, the pressure fluctuations inherent in a V8 engine's exhaust train are reduced. Thanks to a more constant residual-gas content, a higher knock limit and improved bottom-end and mid-range cylinder charging, the shifting camshafts increase the engine's torque and refinement.

The key data for the new E-Class petrol models at a glance:

Modified manual transmission and consumption-optimised automatic

The Mercedes engineers have adapted the tried-and-tested six-speed manual transmission to suit the high torques of the four-cylinder engines. For instance, they equip the new E 250 CDI BlueEFFICIENCY Coupé with a modified transmission which, thanks to more effective gearing and a newly developed dual-mass flywheel, is capable of transmitting the peak torque of 500 Nm with the utmost reliability. On account of the larger gears, the transmission is around 78 millimetres longer than its counterpart for the other four-cylinder models.

The five-speed automatic transmission, available as an option for the four-cylinder CDI Coupé (standard for the E 250 CGI) has likewise been precision-modified by the Mercedes engineers and features a newly developed converter that reduces the hydraulic losses and, therefore, operates even more fuel-efficiently than previously. In "C" mode, the transmission meets the most stringent of requirements in terms of fuel consumption, comfort and output, while "S" mode offers a more sportier configuration with an appropriately adapted gear-change strategy and accelerator pedal characteristic. Optional extras for the AMG Sports package include "M" mode, which has been specially configured for the keenest of drivers.

Standard equipment for the new V6 and V8 E-Class Coupé models includes a seven-speed automatic transmission. In "C" mode, the 7G-TRONIC offers a consumption-optimised transmission mode that is always active after the engine is started.

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