The intake and exhaust valve motion have, as known, a pivotal role in determining engine operation and performances. When dealing with high specific power engines, especially at high rpm, the dynamic behavior of the valve can differ from the kinematic one defined during the design phase. This is related to the high acceleration and forces to which the valve and the other components of the valvetrain system are subjected. In particular, the valve can detach from the cam profile at the end of the opening stroke, and it can show a bouncing behavior during the closing stroke. In addition, all the elements of the valvetrain system are not infinitely rigid and aspects such as the timing chain elongation, the camshaft torsion and the valve stem compression can determine a change in phase with respect to the kinematic one. Since the high complexity level of valvetrains, advanced numerical simulations are mandatory to deeply analyze the behavior of the whole mechanism and each subsystem.
The objective of this study is to develop a one-dimensional model to simulate the valvetrain system of a four-stroke single cylinder engine for racing application. The engine is provided with four valves, and two camshafts. The model is capable of accurately reproducing and predicting the actual motion of valves, including phenomena like valve float and bouncing behaviors at high RPMs. The GT-suite© modeling environment, developed by Gamma Technologies, is utilized for this purpose. The work focuses on modeling various elements of the valvetrain system and provides a thorough account of model calibration using experimental data, including a sensitivity analysis of key model parameters. Modeled elements include the valve itself, the camshaft, chain gears, timing chain, and sliders. By evaluating real valvetrain behavior, the study enables comparisons between different components, such as various camshaft profiles or valve springs, to ensure the desired valve motion within the designated operating range.