Valve timing control system for internal combustion engine

Claim 1

A valve timing control system comprising: a timing sprocket including a cylindrical body; a camshaft; a sleeve secured to said camshaft and disposed in said cylindrical body and cooperating therewith to define an annular space therebetween; a helical piston assembly movably disposed in said annular space; a floating piston movably disposed in said annular space; an end plug closing one end of said annular space; said floating piston and said end plug cooperating with each other to define therebetween a first chamber in said annular space; said floating piston and said piston assembly cooperating with each other to define therebetween a second chamber in said annular space; means for causing said sleeve to vary an angular position thereof relative to said cylindrical body in response to movement of said helical piston assembly; a hydraulic fluid pump; a valve spool movably disposed in said sleeve, said valve spool having a first position wherein said first and second chambers are drained, a second position wherein said first chamber is allowed to communicate with said hydraulic fluid pump to be supplied with pressurized hydraulic fluid and said second chamber is drained, and a third position wherein said first and second chambers are allowed to communicate with said hydraulic fluid pump to be supplied with the pressurized hydraulic fluid; and an actuator operatively connected to said valve spool for movement of said valve spool among said first, second and third positions.