Design And Function: Pistons
The piston is cast in a light metal alloy consisting mostly of aluminum and silicon. The top ring groove is protected by a cast iron ring carrier to withstand the high pressure that the piston is subjected to. There are outlets on top for intake and exhaust valves. The piston is weight-optimised with weight recess above the piston pin and trapezoidal surface against the connecting rod. Even the piston pin has been optimized for weight. Making it extra short not only minimizes the weight of the pin, but also contributes to reduced piston weight. To control piston temperature, there is controllable piston cooling that is controlled by oil pressure. The amount of cooling to be activated is controlled by a model that is calibrated for optimal fuel consumption and low emissions.
To minimise wear and friction:
- The piston skirt is coated with a graphite polymer, which helps to withstand extreme loads, as well as prevent piston noise during cold starts
- the piston pin slide surfaces are coated with DLC
- the cylinder liner surface is refined by means of an optimized honing process at the assembly plant
- the piston rings' tangential forces have been reduced
- the piston rings are coated with a low friction coating
To withstand increased load and reduced friction without compromising on oil consumption, a new ring package has been developed.
- The upper compression ring is 1.2 mm high, nitrated stainless steel ring. The ring is coated with PVD* technology, which both reduces friction and gives good wear properties.
- The lower compression ring is 1.2 mm high, cast in grey iron with phosphated surface.
- The oil control ring is 1.5 mm high, cast iron two-piece ring with conical shaped mating surfaces against the liner. As on the upper compression ring, the surface is PVD coated*.
*PVD (Physical Vapor Deposition) is a type of surface treatment that is created by ionizing an evenly rotating metal surface while introducing a reactive gas. The process takes place under very low vacuum and in temperatures of 400-600 °C. This forms a thin, strongly adherent coating.