The motion of the intake and exhaust valves plays a pivotal role in determining operational efficiency and performance, especially in high-specific power 4-stroke engines. At high rpm levels, the dynamic behavior of the valve may deviate from the kinematic model established during the design phase. This discrepancy arises due to the high accelerations and forces to which the valve and other components of the valvetrain system are subjected. Notably, under such conditions, the valve may detach from the cam profile at the conclusion of the opening stroke and can exhibit a bouncing behavior during the closing stroke. Moreover, the elasticity of all valvetrain system elements introduces additional complexities. Factors such as timing chain elongation, camshaft carrier deformation, and valve stem compression can contribute to a deviation in phase compared to the initially defined kinematics. Within this context, the direct measurement of the valves motion represents fundamental information for both the identification of abnormal valve lift profiles and providing data for the fine-tuning of numerical models for valvetrain simulation.
The primary objective of this study is to determine the effective valve motion at high rpm in a high-performance single-cylinder 4-stroke engine. To accomplish this, an experimental test bench has been established, capable of operating in the range of 2000-15000 rpm. The setup mainly comprises an electric motor to rotate the engine crankshaft, a rapid laser triangulation sensor to measure valve motion, and an encoder for the crankshaft angular position measurement. The laser sensor is rigidly installed inside the engine block, providing a bottom-up view of the valves motion. The obtained results clearly reveal differences between the ideal kinematic behavior and the actual motion of the valve, with float and bounce phenomena becoming apparent over 10’000 rpm. The critical rpm values, above which deviations from the kinematic behavior occur, are highlighted.