Valve timing control system for internal combustion engine

A valve timing control system for an internal combustion engine, comprising:

• a rotary member rotatable according to engine speed;
• a camshaft assembly rotatably connected to said rotary member for driving at least one of an intake and an exhaust valve of the engine;
• phase angle adjusting means, disposed between said rotary member and said camshaft assembly, for adjusting a phase angle relation between said rotary member and said camshaft assembly over a range of first to second phase angles, the second phase angle being different from the first phase angle by a preselected degree;
• driving means including a fluid power source and a pressure chamber, the fluid power source providing fluid pressure to the pressure chamber to activate said phase angle adjusting means for varying the phase angle relation over the range of the first to second phase angles;
• said phase angle adjusting means including a ring gear assembly having helical gear teeth on outer and inner surfaces thereof which mesh with gear teeth formed on said rotary member and said camshaft assembly, respectively, the ring gear assembly being responsive to elevation in the fluid pressure in the pressure chamber so as to be displaced in an axial direction of the camshaft assembly, thereby varying the phase angle relation over the range of first to second phase angles;
• a fluid pressure supply line fluidly communicating between the fluid power source and the pressure chamber;
• a fluid pressure drain line fluidly communicating between the pressure chamber and a drain port;
• switching means having first and second switching positions, the first switching position establishing the fluid communication between the pressure chamber and the drain port through said fluid pressure drain line so that said phase angle adjusting means varies the phase angle relation toward the first phase angle, the second switching position establishing the fluid communication between the pressure chamber and the fluid power source so that said phase angle adjusting means varies the phase angle relation toward the second phase angle;
• and
• a control unit responsive to variation in engine operating conditions to provide a control signal to said switching means to be switched between the first and second switching positions;
• wherein said camshaft assembly includes a sleeve having gear teeth meshing with the gear teeth formed on the inner surface of said ring gear assembly, said rotary member includes a member rotatably inserted into the sleeve, said rotatably inserted member forming a valve bore, said fluid pressure supply line includes a first fluid passage communicating the pressure chamber with the valve bore and a second fluid passage communicating the valve bore with the fluid power source, said fluid pressure drain line includes said first fluid passage and a third fluid passage communicating the valve bore with the drain port, and said switching means includes a valve spool disposed in the valve bore for displacement between first and second valve positions, the first valve position establishing fluid communication between the first and third fluid passages, while blocking fluid communication between the first and second fluid passages, the second valve position establishing fluid communication between the first and second fluid passages, while blocking fluid communication between the first and third fluid passages, said switching means further including an actuator for displacing the valve spool between the first and second valve positions.