Press Release
New SLK V6 Engine from Mercedes-Benz
Systematic fuel economy: heat management in every situation
Mercedes engineers have also made a further contribution to fuel economy with an intelligent heat management system. Coolant circulation is interrupted during the warm-up phase, for example, so that the engine reaches its normal operating temperature more rapidly. This in turn improves the oil flow and considerably reduces friction in the engine, at the same time lowering the exhaust emissions.
When the engine is warm and under full load, the heat flows are directed in such a way that the engine oil and coolant are always at an optimal temperature. This is ensured by an innovative, electronic map-controlled thermostat which is active in all operating situations.
Use of high-tech materials: benefits of lightweight construction
The cylinder head and crankcase of the new V6 engine are made of aluminium. The pistons, connecting rods and cylinder liners are produced according to the latest design principles which not only contribute to weight reduction, but also have a positive effect on engine responsiveness and smooth running. For the lower the moving masses in the crankcase, the lower the vibration and the more responsive the engine becomes to movements of the accelerator pedal:
- The pistons are of iron-coated aluminium. Taking into account the valve angle (28.5 degrees), the piston crowns are designed to ensure a favourable combustion chamber shape.
- Mercedes engineers have been able to reduce the weight of the forged steel connecting rods by approx. 20 percent compared to other V6 engines, thereby making a significant contribution to the extreme smoothness of the new six-cylinder power unit.
- The cylinder liners benefit from low-friction surfaces using aluminium-silicon technology which has also proved its worth in other Mercedes-Benz car engines. Other advantages include minimal distortion, exemplary thermal flows and low weight. The weight saving compared to conventional cast-iron liners is approx. 500 grams per cylinder.
- The forged crankshaft is equipped with four counterweights. Four wide crankshaft bearings attached to the crankcase by transverse reinforcing struts also contribute to reduced vibrations.
- A balancer shaft between the two banks of cylinders compensates the free vibrations inherent to a V6 engine and ensures exemplary smoothness. It counter-rotates at the same speed as the crankshaft.
Audible progress: reduced noise and a designed-in exhaust note
In addition to outstanding output and torque characteristics, a low fuel consumption and extremely smooth running, the new V6 engine also offers tangible advantages in terms of noise comfort. Mercedes engineers have devoted a great deal of technical effort to an acoustic examination of the loudness and frequency generated by each of the approx. 210 components of the engine ??????????????????????????????????????? from the crankcase to the engine mounting, from pistons to injection valves.
Their aim was to achieve pleasant noise characteristics in any driving situation. To do this they not only measured the absolute noise levels as they arose, but also eliminated those sources of acoustic disturbances which may not be very loud, but have unpleasantly obtrusive frequencies as the engine load or engine speed changes - with a negative effect on subjective noise perception.
The acoustics experts also paid special attention to the air intake, and for good reasons: the intake noise of an engine tends to spread towards the vehicle interior across its entire spectrum, and can therefore adversely affect the noise comfort of the occupants. One result of the sophisticated analytical work, using the latest measuring procedures corresponding to actual hearing perception, was the development of intake ducts of woven nylon. In contrast to the smooth-surfaced plastics used previously, this material has a sound-absorbing effect and significantly reduces intake noise.
The subject of noise configuration is increasingly becoming a major aspect of engine development, especially as engineers are required to resolve the conflict of aims between a low level of drive-past noise and a pleasant, throaty exhaust note. In the new six-cylinder unit for the SLK-Class the specialists in Stuttgart strictly followed the concept of reducing noise and designing sound. For this reason various measures were developed to reduce the engine noises - from a twin-cartridge air filter with integral resonators to a sound-absorbent mat under the bonnet. At the same time the sound specialists devoted attention to creating the typical sports car sound of the SLK-Class by emphasising certain pleasant frequencies, especially by careful configuration of the exhaust system. The results are well worth hearing.
Emission control on a dual basis: emissions below the EU 4 limits
In common with all recent Mercedes-Benz petrol engines for cars, the new V6 for the new SLK-Class already meets the stringent EU 4 exhaust emission limits which come into force from 2005.
The emission control system follows a two-stage concept: it is based both on sophisticated engine-specific measures for a reduction in untreated emissions and on highly effective emission control using catalytic converters positioned close to the engine. Each of these is equipped with two oxygen sensors - a control sensor and a diagnostic sensor - with linear control. This means that the oxygen sensors are already active immediately after a cold start, supplying information about the exhaust gas constituents for the electronic engine management system to process when controlling the warm-up phase. This enables the catalytic converters to reach their normal operating temperature more rapidly.
The engine-specific measures include for example variable camshaft adjustment, which makes efficient internal exhaust gas recirculation possible under partial load. In the same way the adjustable tumble flaps in the intake ducts, which improve the combustion process, make an important contribution to minimizing the untreated engine emissions.
A secondary air injection system is also used. This has an afterburning action on the exhaust gases, increasing the temperature in the exhaust ducts and enabling the catalytic converter to start converting the pollutants at an earlier stage. During this afterburning process the carbon monoxide and hydrocarbon content in the untreated exhaust gases is also reduced.
