Internal combustion engine noise is primarily composed of combustion and mechanical noise shares. Mechanical noise contributions in engines have increased relevance at low load conditions when combustion related noise is not significant. Current literature on mechanical noise in engines includes: piston pin ticking, piston secondary motion, and valvetrain impacts. A mechanical noise source from excitation of piston tertiary motion is described here in the form of a case study on an engine exhibiting a cold start “clatter” noise.
Targeted experimental measurements were initially used to rule out potential mechanisms such as impacts resulting from piston pin ticking and piston secondary motion. Experimental modification studies and piston load and kinematics modeling led to discovery of instability of the piston which is understood to excite tertiary motion of the piston and result in impulsive “clatter” noise under certain low load/speed conditions. The results of the tests and analyses conducted to address the clatter noise are discussed, after which suitable conclusions are drawn.