Improvement of DOHC Valve Train Noise by Analysis of Valve and Tappet Movement

The noise generation mechanism of a direct-acting valve train such as used in sporty and luxury cars was determined for both mechanical and hydraulic tappets through measurements of sound pressure levels and vibrations and the use of computer graphics to observe actual valve and tappet movement.

Two phenomena were clarified: chatter at low engine speeds and a mechanical noise at high engine speeds. Further experiments established that the noise of a mechanical tappet can be greatly reduced and its tonal quality improved by optimizing the cam profile and by increasing the acoustic damping ratio of the tappet.