Valve timing control system for internal combustion engine

A valve timing control system for an internal combustion engine which has a crank shaft and a cam shaft operatively connected with said crank shaft so as to rotate in synchronism therewith whereby intake and exhaust valves are driven to open and close by virtue of a valve operating mechanism mounted on said cam shaft in synchronism with the rotation of said crank shaft, said valve timing control system comprising:

• variable valve timing means for advancing and retarding a cam angle with respect to a crank angle;
• advance amount calculating means for calculating an advance amount being a phase difference between said cam angle and said crank angle;
• required advance amount calculating means for calculating a required advance amount on the basis of an operating condition of said internal combustion engine;
• valve timing control means for calculating a valve timing control variable, for driving said variable valve timing means, on the basis of said advance amount calculated by said advance amount calculating means and said required advance amount calculated by said required advance amount calculating means, and further for controlling said variable valve timing means on the basis of the calculated valve timing control variable;
• and
• time period measuring means for measuring an elapsed time after start of said internal combustion engine,
• wherein said required advance amount calculating means makes a calculation so that said required advance amount assumes a value smaller than that in a normal state until said time period measuring means measures a predetermined period of time.