The new Mercedes-Benz SLK: Passion meets efficiency - Daimler

Four-cylinder with a bitePage 26The four-cylinder engines for the new SLK follow the so-called downsizingprinciple, with the reduced cubic capacity compensated by homogeneous directinjection and turbocharging. This leads to advantages such as lower weight andreduced in-engine friction. A smaller engine also moves the operating range ofthe characteristic map towards more favourable values, with consequent fuelconsumption benefits.The direct injection system of the four-cylinder engines has an injectionpressure of up to 140 bar. In the interests of improved efficiency, this allowsthe compression ratio to be increased versus a conventional duct injectionsystem. The fuel evaporating directly in the combustion chamber also lowersthe temperature in the combustion chamber, reducing the engine's tendencyto knock. The engine is homogeneously charged.The same turbine rotors are used to generate charge pressure in both outputvariants of the four-cylinder engine. The single-flow turbocharging of thefour-cylinder units operates more efficiently than a mechanical charger,as no engine output needs to be devoted to the charger.Other characteristics of the four-cylinder engines include a four-valve conceptwith forged intake and exhaust camshafts, as well as camshaft adjustment onthe vane-cell principle. This enables the valve timing to be rapidly and variablyadjusted. The result is high torque even at low engine speeds, and a higherspecific output.The crankcase and cylinder head are cast from aluminium alloy. Thecrankshaft is likewise cast, and has eight counterweights. To compensate thesecondary masses inherent to a four-cylinder in-line engine, two Lanchesterbalancer shafts rotate within the crankcase at twice the crankshaft speed.An electronically controlled thermostat ensures logic-controlled engine warmup(no coolant flows through the cylinder head when the engine is cold), andtherefore intelligent thermal management. The warm-up phase is shortened asa result.Daimler Communications, 70546 Stuttgart/GermanyMercedes-Benz – A Daimler Brand