مهراب اسدی

Valvetrain is one of the major sources of noise and vibration in IC engines. The importance of cam surface quality parameters is highlighted in the valve train mechanisms with direct sliding contact between cam and tappet. In this paper, the influence of surface quality parameters on high frequency noise producing is investigated. The roughness and waviness of some intake and exhaust camshafts with diverse surface qualities were measured and then were mounted on a four cylinder gasoline engine to measure the noise level of valvetrain mechanism through NVH analysis. Furthermore, the characteristics of the unusual sound which is considered as an annoying noise were determined also, the camshaft Surface topology was inspected by a Scanning electron microscope (SEM). The results show that the nonconformities in surface parameters such as roughness and waviness are the main factors that lead to producing high frequency annoying noise and therefore must be carefully considered by designer.

Timing belts transmit crankshaft's power to rotate synchronously camshafts so that the engine's valves open and close at the proper times. Various vibrations will be imposed to timing belt during engine operation that could lead to movement and flapping of timing belt. Lateral belt tracking that pushes belt toward or outward of engine is one of these movements. This movement cause to improper contact between pulley's flange and timing belt that can produce annoyance noise and also accelerate the belt failure. There are many factors such as starting temperature, inclination of pulleys, inherent characteristics of belt, belt width, and position of tensioner which effect on belt tracking. This article evaluates effect of starting time, belt width and belt run-off on magnitude of lateral force in an internal combustion engine. According to test results, reducing starting temperature to lower than 30 C has considerable effect on rise of lateral force and belt movement. By 0.5 increase of belt width can reduce lateral force acceptably. Moreover, it is possible to control lateral movement by using timing belts with proper run-off.