Abstract
Keywords
Friction, Piston, Valve-train, Shimless, Combustion
Abstract
The friction reduction is a very challenging theme of research and development on reciprocating engines, and in particular on engines for passenger cars, while is very attractive to reduce the engine fuel consumption and thus CO2 emissions. The points of improvement are several: valve train and timing command, piston package, liners, crankshaft, ancillaries and related command, lubrication, cooling, and involve optimisation of couplings, components design, materials, manufacturing technology, etc.
This paper presents a comprehensive activity of engine development, which starts from considerations about the single contribution of each engines functional group on total friction, selects the fields of research where the most effective results can be expected, and concludes with results obtained on a Demonstration Engine.
The fuel consumption reduction obtained very significant, especially at low engine speed and load, which means in the real-life vehicle urban drive; a reduction of about 7÷8% is expected on vehicle in the NEDC.
The main themes of development have been: a new lightened valve train, also featuring shimless mechanical tappets; and a new piston package, which includes a piston with only two segments, a newly designed con-rod and a lightened piston pin. The range of FMEP reduction obtained is about 10÷26% w.r.t. base engine over the whole engine speed and load map, with the strongest effect in the low speed and load range.
Also functionality and durability of the new components have been tested and validated. In particular, the new two-segment pistons have been optimised for blow-by and oil consumption, obtaining results equal to or lower than the standard package. Both the piston package and the new lightened valve-train have been tested for durability, with procedures usually required for production validation.