Acoustical Optimization of the Piston Slap by Combination of Computing and Experiments

Basic investigations were carried out on two direct-injection diesel engines regarding the subject “noise excitation through piston slap”.

To provide an acoustically optimized piston, the impact of the top land must be eliminated and the skirt impact lessened. Examples of favourable piston design are reduction of the piston to cylinder clearance, increase in the top land clearance, increase in the guiding skirt length and increase in stiffness in the lower skirt area. Maximum influence of piston design manifests itself in the structure vibration signals, measured on the cylinder liner, in the frequency range between 4 and 8 kHz. Good agreement was observed for all piston versions between the results of structure vibration measurements and those of the secondary piston movement.

No agreement could be observed between the cylinder pressure and the liner vibrations in terms of frequency.