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

An intake- and/or exhaust-valve timing control system for an internal combustion engine comprising:

• a rotating member having a driven connection with a crankshaft of said engine;
• a camshaft journaled by a bearing member mounted on a cylinder head and receiving torque transmitted from said rotating member;
• a phase-angle adjusting mechanism for adjusting a relative phase angle between said rotating member and said camshaft;
• a first hydraulic circuit provided for drivingly controlling said phase-angle adjusting mechanism via fluid pressure depending upon the operating state of said engine;
• a second hydraulic circuit provided for lubricating frictional surfaces between said bearing member and said camshaft, said first and second hydraulic circuits being separated from each other;
• a directional control valve connected to said first hydraulic circuit for switching the direction of working fluid flowing through said first hydraulic circuit;
• said first hydraulic circuit including a supply and drain fluid passage serving as both oil supply passage and oil drain passage, said second hydraulic circuit including a lubricating oil passage, said supply and drain fluid passage and said lubricating oil passage both being disposed in said cylinder head;
• and
• said lubricating oil passage including at least two oil ducts, respectively arranged at both sides of said supply and drain fluid passage in an axial direction of said camshaft, in order to enhance a lubricating efficiency.