Valve timing control system for internal combustion engine

摘要

A valve timing control system for accelerating activation of a catalytic converter in an internal combustion engine in a cold starting operation mode while enhancing control accuracy by learning a reference position of a cam angle. The system includes actuators (15; 16) coupled to cam shafts (15C; 16C), respectively, hydraulic pressure supply means (19; 20) for driving the actuators (15; 16), and a controller (21A) for controlling hydraulic pressure fed to the actuators (15; 16) in dependence on engine operation states to change phases of the cam shafts (15C; 16C) relative to a crank shaft (13C). The controller (21A) is so designed as to set a valve timing to a most advanced position or alternatively to a most retarded position in a cold-state idling operation mode for the purpose of learning a reference position.