Modular approach for valve train dynamics and friction simulation with in situ experimental validation

The study presents experimental and theoretical investigations of the friction losses in the valve train of an internal combustion engine. To avoid extraneous factors introduced by the simulating test rigs, the experimental investigation is conducted on a running single cylinder engine.; Original techniques are developed to isolate and measure the friction losses between valve train components, and to theoretical model them. A specially modified tappet was designed, and manufactured, to measure the friction force between the cam and the tappet, and the friction force between the tappet and the tappet bore.; A simplified elasto-hydrodynamic (EHD) model is proposed for the Cam-Tappet friction. Existing EHD models predict, and experimental measurements confirm, a very small value for the oil film (OFT) thickness. The exponential increase of the oil viscosity with pressure, in the highly loaded Hertzian contact, determines a non-Newtonian behavior for the entrapped oil. Subsequently the OFT plays a secondary role on the friction force, the primary role being transferred to the contact between two rough surfaces, and to the rehological properties of the oil.; The cam-tappet EHD model was applied in three steps, corresponding to successive degreed of accuracy. (1) Cam-tappet friction model neglecting that tappet spin; (2) Cam-tappet friction model considering the tappet spin; (3) Cam-tappet friction model considering the tappet spin.; It was found that the cam-tappet contact friction force is responsible for most of the energy lost during the valve train operation. The rocker arm bearing friction is responsible for 10–11% of the valve train friction, and the valve stem-valve guide is responsible for 1–2% of the valve train friction.