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The new V6 engine in the E-Class: Power to spare
- Fuel consumption lowered by up to six percent despite more output
- Powerful torque of 350 Nm between 2400 and 5000 rpm
Output, torque, fuel consumption, comfort and exhaust emissions – these were the task areas – all of them equally important – during the development of the V6 engine in the new E 350. The up-to-date six-cylinder unit sets standards in each of these disciplines, offering technical innovations which do not constitute individual solutions but have a positive effect on various aspects.
Mercedes engineers already created important conditions for exemplary perform-ance characteristics with four-valve technology and the four overhead camshafts, but this was not enough in itself. They also developed a system which enables the interaction of the 24 valves to be controlled according to need – depending on the engine load – and which ensures a split-second gas exchange in the cylinders: continuously variable camshaft adjustment. This means that the angles of both the intake and exhaust camshafts can be continuously varied by 40 degrees to make sure that the valves open and close at the most favourable point in any driving situation.
At low engine loads this technology is used to direct exhaust gases back to the intake manifold from the combustion chamber. To achieve this, the camshafts are controlled in such a way that the exhaust valves remain open for a short time while the intake valves are opening. During this brief period a portion of the exhaust gases is able to escape from the exhaust to the intake duct, assisted by the vacuum pressure in the intake manifold. This valve overlap when venting the used gases and taking in the fresh mixture enables an efficient internal exhaust gas recirculation process to take place. This reduces the energy losses during load changes in the cylinders – resulting in a significantly lower fuel consumption.
At higher engine loads the camshaft adjustment is used to optimise the valve overlap as a function of the engine speed in such a way that the combustion chambers are optimally supplied with fresh mixture – thus ensuring a high output and torque.
The camshafts are controlled by electrohydraulically operated vanetype actuators. These are located at the front ends of the camshafts and are controlled by four integral hydraulic valves. The intake camshafts are driven by a duplex chain, while the exhaust camshafts are driven directly by the intake camshafts via a pair of gears. In addition to the four-fold, variable camshaft adjustment system, a number of other features contribute to the exemplary performance characteristics of the V6 engine:
- Flow-optimised intake ducts with innovative tumble flaps for the best possible throughput
- Specially developed valves with a shaft diameter of only six millimetres, which only slightly disturb the flow in the intake duct
- Compact combustion chambers for high compression (10.7:1) and good volumetric efficiency
- The newly developed, two-stage variable intake manifold.
The intake module is produced in well-proven magnesium and allows the air intake to be varied according to the load conditions and engine speed. The length of the intake ducts leading to the cylinders is altered by means of flaps: at high engine speeds – from approx. 3500 rpm – the flaps are open and the air flows into the combustion chambers over a short distance, producing a high output. At low engine speeds the flaps are closed to increase the length of the intake duct. This produces pressure waves which support the intake process and significantly improve the torque yield in the lower engine speed range. 305 Newton metres of torque – 87 percent of the maximum – is already available from 1500 rpm.
Turbulent airflow: tumble-flaps in the intake ducts
The special feature of the intake manifold in the Mercedes six-cylinder engine is the electropneumatically driven flaps at the end of each intake duct. These make a considerable contribution to fuel economy. Mercedes engineers refer to these as tumble-flaps, which describes their function: they literally cause the fuel/air mixture to tumble, thereby increasing the turbulence of the airflow and allowing it to reach the combustion chambers at a higher speed for more even distribution. The result is more efficient and complete combustion.
Under partial load the tumble-flaps swivel up, optimise the airflow and thereby increase the speed of combustion – an advantage which is particularly noticeable in view of the leaner mixture caused by exhaust gas recirculation and which reduces the fuel consumption. The tumble flaps are not required under higher engine loads, therefore they are fully recessed into the intake manifold and do not disturb the intake process. This situation-related control of the tumble-flaps is based on a prestored, logic-controlled microcomputer program.
Thanks to the tumble-flaps in the intake ducts, the fuel consumption of the V6 engine can be reduced by up to 0.2 litres per 100 kilometres depending on the engine speed – while improving smoothness at the same time.
Combustion of the fuel/air mixture is via a direct coil ignition system. The spark plugs project into the cylinders from a central position between the four valves, with the ignition coils arranged immediately above them.
The tumble-flaps, fuel injection, ignition and numerous other engine functions are controlled by the Bosch ME 9.7 engine management system, which communicates and exchanges information with the other onboard electronic control units via a databus. In the interests of short electrical paths, the engine management unit is centrally located above the intake system and integrated into the engine design.
The microprocessor in the control unit continuously diagnoses all engine functions. This includes monitoring of the catalytic converters and ignition system, electrical checks on the purge valve and controlling the lambda sensors. Should one these major emission control systems develop a fault, the warning "Check Engine" appears in the instrument cluster display. The data are stored in memory at the same time, allowing service technicians to identify the cause at once and remedy the fault.
Mercedes engineers have made a further contribution to fuel economy with an in-telligent heat management system. For example, circulation of the coolant is prevented during the warm-up phase so that the engine reaches its normal operating temperature more rapidly. This leads to an improved oil flow and therefore significantly less friction within the engine. Exhaust emissions are also reduced as a result. Even when the engine is warm and under full load, the heat flows are controlled to ensure that the engine oil and coolant are always at their ideal temperature. This is done by a new, logic-controlled thermostat which is active under all operating conditions.
Progress in figures: more driving pleasure, lower fuel consumption
A comparison between the new E 350 and the previous E 320 shows the positive effects of the new technology in the V6 engine on performance and fuel consumption:
- Acceleration from 0 –100 km/h: The E 350 Saloon takes 6.9 seconds to reach 100 km/h from standstill, which is 0.8 seconds faster than its predecessor. The acceleration time for the Estate is 1.4 seconds shorter than for its predecessor, at 7.1 seconds.
- Flexibility: The new E 350 Saloon absolves an intermediate sprint from 60 to 120 km/h in 6.9 seconds, and is therefore 1.7 faster than the E 320. The Estate takes 7.2 seconds, which is 2.2 seconds less than the preceding model.
- Maximum speed: The maximum speed of the Saloon is increased from 245 to 250 km/h, and that of the Estate from 233 to 250 km/h (electronically limited).
- Fuel consumption: Despite the 21 percent higher output of the new V6 engine, the fuel consumption of the Saloon is reduced by 0.2 to 9.7 litres per 100 kilometres compared to the E 320 (NEDC combined consumption). For the Estate the fuel saving is 0.7 litres per 100 kilometres.
(figures for the Estate in brackets)
|Valves per cylinder||4|
|Compression ratio||10.7 : 1|
|Output||200 kW/272 hp at 6000 rpm|
|Max. torque||350 Nm at 2400-5000 rpm|
|0–100 km/h||6.9 s (7.1 s)|
|Maximum speed||250 km/h*|
|NEDC combined consumption||9.7 l/100 km (9.9 l/100 km)|
Lightweight construction: aluminium crankcase and cylinder head
The cylinder head and crankcase of the new V6 engine are of aluminium. The pistons, connecting rods and cylinder liners also reflect the latest design principles, which not only contribute to weight reduction but also have a noticeably positive effect in terms of responsiveness and smooth running. The lower the moving masses in the crankcase, the lower the vibrations and the more agile the engine’s response to movements of the accelerator.
The pistons are made of iron-coated aluminium. Taking the valve angle (28.5 degrees) into account, their crowns are shaped to provide a favourable combustion chamber.
- Mercedes engineers have reduced the weight of the forged steel connecting rods by around 20 percent compared to other V6 engines, thereby making a major contribution to the refined running characteristics of the new six-cylinder unit.
- The cylinder liners feature low-friction surfaces in aluminium-silicon technology, a system which has proved successful in other car engines by Mercedes-Benz. Other advantages include high dimensional stability, exemplary thermal characteristics and low weight. The weight saving compared to conventional cast-iron liners is approx. 500 grams per cylinder.
- The forged crankshaft is fitted with four counterweights. Four wide crank-shaft bearings with transverse reinforcements attached to the crankcase likewise ensure that vibrations are reduced.
- A balancer shaft between the two banks of cylinders compensates the free vibrations that are inherent to a V6 engine and ensures exemplary smoothness. It counter-rotates with the crankshaft at the same speed.
Audible comfort: noise reduction and sound engineering
In addition to exemplary output and torque characteristics, a favourable fuel consumption and smooth running, the new V6 engine offers audible progress. Where noise comfort is concerned, Mercedes engineers have devoted a great deal of technical effort towards the engine’s acoustics, assessing the volume and frequency of the noise emitted by practically each one of the approx. 210 individual components in the engine – from the crankcase to the engine mountings, and from the pistons to the injection nozzles.
Their aim was to achieve a pleasant noise background in any driving situation. To make this possible they not only measured the absolute noise values, but also eliminated sources of acoustic disturbance which are not particularly loud in themselves, but can become unpleasantly obtrusive with specific frequencies during load or engine speed changes – and which worsen the subjective impression of noise. The air intake system is a good example: as a result of the analyses carried out with the latest measuring techniques, the intake ducts are made from woven Nylon. In contrast to the smooth plastic used previously, this material has a sound-absorbing effect and significantly reduces the intake noise.
The subject of noise engineering is increasingly becoming a major task of engine developers, especially since engineers are called upon to resolve the conflict of aims between a low level of drive-by noise and a pleasant, throaty exhaust note. In the case of the new six-cylinder engine the specialists followed a concept of reducing noise while designing the sound. Various measures were therefore adopted to reduce engine noise – from a twin-cartridge air filter with integral resonators to a sound-absorbing mat beneath the bonnet. At the same time the specialists went to work on producing a sonorous six-cylinder sound by emphasising certain pleasant frequencies – especially by specific configuration of the twin-pipe exhaust system.
Two-stage concept: emission control in the engine and by catalytic converters
The emission control concept has a two-stage structure. It is based firstly on sophisticated in-engine features which ensure a low level of untreated emissions, and secondly on a highly effective exhaust gas treatment system using two 1.4-litre near-engine catalytic converters. Each of these is equipped with two lambda sensors - one control and one diagnostic sensor - and is in a linear closed loop. This means that the lambda sensors are already active immediately after the engine is started, providing information about the exhaust gas constituents which the electronic control unit processes to ensure an efficient warm-up phase. The catalytic converters also reach their normal operating temperature more rapidly thanks to the air-gap-insulated, stainless steel exhaust manifold.
The in-engine systems include variable camshaft adjustment, which makes efficient internal exhaust gas recirculation possible under part-throttle conditions. The adjustable tumble-flaps in the intake ducts of the V6 engine, which improve the combustion process, also make a major contribution to minimising the engine’s untreated emissions. A secondary air injection system is also used. This has an afterburning effect on the exhaust gases, raising the temperature in the exhaust ducts and enabling the catalytic converter to convert pollutant emissions at an earlier stage. This thermal afterburning also reduces the proportion of carbon monoxide and hydrocarbons in the exhaust gases.
Perfect partner: seven-speed automatic transmission as standard
The powerful V6 engine and the 7G-TRONIC seven-speed automatic transmission are a formidable team on board the new E 350. Thanks to a number of special technical features, this transmission enables the characteristics of the six-cylinder engine to be fully exploited and makes an important contribution to powerful acceleration, fast intermediate sprints, a favourable fuel consumption and a high level of gearshift comfort.
The special qualities of the world’s first seven-speed automatic transmission for passenger cars are due to a number of design features. The most important is the increase in forward gears from the previous five to seven. This allows a wider spread of ratios, as well as further reducing the differences in engine speed between the individual gears achieved by the five-speed transmission. As a result, the driver can rely on having the optimum ratio at his or her disposal for virtually any driving situation. In addition, the electronic control unit has even more scope with which to optimise the shift processes to achieve lower fuel consumption and greater comfort. For example, at 100 km/h the engine speed will be on average – depending on the driving situation - around twelve percent lower than with a five-speed automatic. This impressive engine speed adjustment system opens the door to lower noise, as well as improved fuel economy.
Mercedes engineers have achieved further important advances where shift control is concerned: if the driver needs to accelerate quickly and therefore change down rapidly through several gears - i.e. kick-down - 7G-TRONIC avoids having to move through the gears in strict order. Instead, the transmission uses its direct downshift capability, shifting down by as many as four gears – as the situation requires – rather than just one at a time. Shift times have been reduced significantly below the levels of the previous five-speed automatic transmission.
The seven-speed automatic transmission also features a torque converter lockup clutch. This is located in the hydrodynamic torque converter and largely eliminates slip between the impeller and the turbine wheel in many operating situations. It manages this by establishing – where possible – a virtually rigid connection between the engine and transmission shafts, thus preventing power losses. In contrast to conventional automatic transmissions, where the converter can only be locked up in higher gears, the lock-up clutch in the seven-speed automatic transmission by Mercedes-Benz is already active in first gear. In addition, in the interests of comfort, the torque converter lock-up clutch features slip control, which allows it to run extremely smoothly. This is another way in which Mercedes engineers have achieved optimal shift quality.
Gear changes at the touch of a button: optional gearshift buttons on the steering wheel
In order to tap into the remarkable performance of the six-cylinder engine rapidly and smoothly in any driving situation, 7G-TRONIC can also be operated by means of optionally available gearshift buttons on the steering wheel.
In addition to this manual mode, drivers can also make use of the "C" (Comfort) and "S" (Sport) settings, in which the gears are shifted automatically. The "S" mode is configured for a particularly sporty driving style, and the movements of the accelerator pedal are transmitted more directly. In "C" mode a comparatively lower gearshift frequency intentionally brings about a particularly calm, relaxed style of driving.
Good traction: E 350 also available with 4MATIC
Mercedes-Benz also offers the new E 350 with the option of 4MATIC permanent four-wheel drive and a five-speed automatic transmission. By interacting intelligently with the standard Electronic Stability Program ESP® and the electronic traction control system 4ETS, 4MATIC helps the driver to manage critical situations safely and confidently. In adverse weather conditions with snow, ice or wet roads, for example, as well as when moving off, accelerating or driving on loose surfaces, the 4MATIC models by Mercedes-Benz ensure an even higher level of traction and dynamism. Moreover, 4ETS guarantees typical Mercedes ride comfort because the system operates without the conventional differential locks which tend to impair comfort and handling in other four-wheel drive cars. Instead 4ETS applies specific brake pressure to spinning wheels, directing the drive torque to the wheels which still have good traction. In this way electronic traction control achieves the effect of three differential locks.