Fuel consumption significantly reduced

With NEDC fuel consumption values between 6.9 and 7.9 litres per 100 kilometres (combined consumption), the petrol models in the Mercedes-Benz A-Class have always been among the most economical cars in their class. The new A-Class will consolidate this position even further. The specific fuel consumption of the spark-ignition engines has been lowered by reducing friction losses in the piston, connecting rod and valve control systems, as well as by further improvements to the mixture distribution in the combustion chambers. In practical terms this means that in the NEDC test, the petrol models in the new A-Class will consume less fuel than their predecessors despite a higher output.

The up-to-the-minute, lightweight power unit consists of an aluminium crankcase with grey cast iron cylinder liners. The pistons, sump, oil pump, rocker arms, engine mounting, timing case and other engine components are also of aluminium, while the intake manifold, air filter and cylinder head cover are made from plastic. Depending on the displacement, and thanks to this lightweight design, the petrol engines tip the scales at only 92 (A 150) to 117 kilograms (A 200 TURBO) and are therefore significantly lighter than other four-cylinder units in this displacement class. The power-to-weight ratio of the turbocharged engine is a remarkable 0.82 kilograms per Kilowatt.

The compact cylinder head features a swirl duct which creates high turbulence in the fuel/air mixture, thereby ensuring an optimal combustion process. The central location of the spark plugs serves the same purpose. Valve control is by a hollow camshaft of induction-hardened forged steel and low-friction rocker arms. A timing chain with a hydraulic tensioner and rubber-coated sprockets drives the camshaft. A hydraulic system automatically controls valve clearance compensation.

Mercedes engineers have also achieved the high thermal efficiency of the spark-ignition engines with a high compression ratio of 11.0 : 1. This made it necessary to divide the water jacket into two sections: the lower section has a high speed of flow in order to cool the very hot combustion chamber areas – especially the webs between the intake valves – and therefore make this high compression ratio possible in the first place. The upper section cools the engine’s valve control system. In addition the exhaust valves of the A 170, A 200 and A 200 TURBO are sodium-cooled.