The M133 is a 4-cylinder petrol engine with turbocharging developed independently by Mercedes-AMG and based on the M270 by Mercedes-Benz. All of the components relevant to performance and strength have been newly developed and optimised. The high-performance M156 and M157 engines served as technical role models and as a result many of the findings won from them have been integrated into the development of the M133. The engine will be used first in the A 45 AMG and as the most powerful series production four cylinder turbo engine with an output of 265 kW and 450 Nm torque will take the pole position in the competition segment.
The all-aluminium crankcase is manufactured in a cast aluminium process using forming sand cores. A new two-part water jacket provides for optimum flow through the crankcase. Despite a high ignition pressure of up to 140 bar, use of cast iron is unnecessary thanks to the strength-optimised load paths in the crankcase between the cylinder head and the crankshaft bearing cap as well as the closed-deck design. The result is a weight to performance ratio which is outstanding for a sports engine. Pulsation bores above the bearing blocks connect adjacent crankcase cavities, ensuring that pressure is balanced efficiently and in turn reducing inner pumping losses. The NANOSLIDE technology for the coating of the cylinder contact surfaces was adopted from the SLS AMG.
After being coated, the contact surfaces undergo torque plate honing. This means that the mechanical surface treatment is carried out when the barrels are bolted in place. This thus eliminates any static distortion caused in the cylinder contact surfaces by tightening the cylinder head bolts. A low-friction coating is also applied to the piston rings. As a result, frictional losses are reduced, oil consumption is lower and fuel consumption is improved.
Integrated channels next to all of the cylinders mean that all of the oil returns directly to the oil pan which ensures oil supply in all states of acceleration.
A weight-optimised crank assembly is located in the interior. As the specific output is high at 132.5 kW/l the crankshaft, connecting rod and pistons were forged, a construction that is otherwise used in motor racing.
Two overhead camshafts each actuate two exhaust and two intake valves per cylinder via low-friction, low-maintenance cam followers. The exhaust valves are thermally heavily loaded and are hollow-bored and filled with sodium for cooling purposes.
The M133 makes use of the advantages of spray-guided direct injection of petrol. Thanks to greater thermodynamic efficiency, this technology makes it possible to use fuel more efficiently which results in lower emissions.
To meet demands appropriately, the fuel injection pressure reaches up to 200 bar by using a single-plunger high-pressure pump with an integrated flow control valve. The fuel is conveyed via a high-pressure rail to the piezo injectors which are centrally located in the four combustion chambers. Using multi-injection technology, the quantity of fuel can be metered to suit demand and combustion can also be accordingly controlled.
Turbocharging is by means of a twin-scroll turbocharger with up to 1.8 bar. The exhaust gas ducts of cylinder pairs merge to form a flow-optimised manifold. The advantages of the special twin-scroll manifold are: The pressure and temperature levels as well as the kinetic energy of the exhaust gas provide for an optimum gas cycle and a fast response despite the high degree of supercharging. The tendency to knock and the proportion of residual gas in the cylinders are also minimised.
Great importance was placed on low-loss implementation for the air intake as a whole. The large round air filter is located directly upstream of the turbocharger. The air is conducted directly to the intake side via the air-water intercooler and from there it travels the short distance to the charge-air distributor. The charge air is cooled by means of its own coolant circuit which provides cooling down to 130°C.
The valve timings of the intake and exhaust valves are adjusted via continuously variable camshaft positioners, whereby an optimum cylinder charge is achieved at each operating point. Scavenging occurs at the lower end of the engine speed range. This means that the opening times of the intake and exhaust valves overlap and the exhaust gas is flushed out of the cylinder with the intake air which in turn increases cylinder charging. Furthermore, the increase in mass flow rate leads to improved turbocharger response and reduced turbo lag.
Various measures designed to increase efficiency have been implemented in the M133. These include for example, alternator management, on-demand control of the oil pump and the ECO start/stop function. With its use of the twin-scroll turbocharger, the engine's design provides for an early response and high torque even at low engine speeds. Thus the maximum torque of 450 Nm is already available at an engine speed of 2250 rpm. This, together with the inner-engine measures, means that fuel consumption is only 6.9 l/100 km and CO2 emissions are only 161 g CO2/km according to the NEDC. This also means that the M133 is at the top of its segment. Furthermore, due to particularly low exhaust emissions, the M133 now already complies with the Euro 6 emissions standard which only comes into effect in 2015.
Key figures at a glance:
|Valves per cylinder||4|
|Output||265 kW (360 hp) at 5500 rpm|
|Max. torque||450 Nm at 2250-5000 rpm|
|Maximum engine speed||6700 rpm|
|Fuel consumption NEDC combined||6.9 - 7.1 l/100 km|
|CO2 emissions||161 - 165 g/km|