Press Release
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 performance 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:
The developers of the V6 devoted great attention to all measures which would contribute to the best possible aspiration of the engine. Powerful computer programmes assisted with the flow calculations, helping for instance to optimise the intake air flow from the dual-flow air filter, where the lines come together at the hot-film air flow sensor (HFM). For an efficient airflow, its housing is oval in shape and accommodates an electrically heated sensor which determines the intake air mass and provides the engine computer with important information for the composition of the fuel/air mixture.
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 intelligent 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:
