Intake- and/or exhaust-valve timing control system for internal

Abstract

An intake- and/or exhaust-valve timing control system for internal combustion engines comprises a timing pulley including inner and outer gears, a camshaft including an outer gear and a ring gear disposed between the pulley and the camshaft for varying the phase angle between the camshaft and the pulley. The ring gear includes inner and outer gears respectively meshed with the outer gear of the camshaft and the inner gear of the pulley. At least one of the two meshing pairs of gears is helical. The outer gear of the pulley has a first number of teeth and the outer gear of the camshaft or the ring gear has a second number of teeth different from the first number, and a combination of the first and second numbers is selected in such a manner as to satisfy an inequaltiy .vertline.dO+n(360.degree./M).vertline..ltoreq..vertline.T.vertline., wherein dO is an offset angle of intake- and/or exhaust-valve timing of the engine in a state wherein the pulley, the camshaft and the ring gear are temporarily assembled, n is an integer, M is the least common multiple between the first and second numbers, and T is a predetermined tolerance for valve timing.