Inverted Tooth Chain Sprocket with Frequency-Modulated Meshing Features to Reduce Camshaft Drive Noise

This paper outlines the design and development of an inverted tooth style sprocket that incorporates tooth profile features to reduce chain drive noise levels by modulating or “staggering” the chain-sprocket meshing impacts. Meshing frequency modulation was achieved by replacing a number of the standard teeth with a tooth form altered to include an offset engaging flank surface to vary the location and the rhythm of the meshing impacts. This altered tooth form was arrayed with the standard teeth in a random or arbitrary pattern in order to create a random meshing sprocket, thus serving to modulate the chain meshing impact frequency compared to that of a standard inverted tooth sprocket having a full complement of symmetrical teeth.

Noise and vibration tests were conducted on a 4-cylinder DOHC non-firing “motored” engine in an anechoic test cell. The tests were done to compare the camshaft drive noise levels for a 24-tooth standard crankshaft sprocket with that of a new 24-tooth random meshing sprocket. The testing confirmed the N&V gains with the random meshing sprocket at meshing frequency (24^th order) and the first harmonic (48^th order) as well as for the overall chain drive noise levels.