Patent ID: 6883475

Claim:
A variable cam timing system for an internal combustion engine having a crankshaft, at least one camshaft, a cam drive connected to the crankshaft, and a variable cam phaser having an inner portion mounted to at least one camshaft and a concentric outer portion connected to the cam drive, the relative angular positions of the inner portion and the outer portion being controllable in response to a fluid control input, such that the relative phase of the crankshaft and at least one camshaft can be shifted by varying the fluid at the fluid control input of the variable cam phaser, the variable cam timing system comprising: a) a spool valve ( 28 ) comprising a spool slidably mounted in a bore at an axis at a center of the inner portion of the variable cam phaser, the bore having a plurality of passages coupled to the fluid control input of the variable cam phaser, such that axial movement of the spool in the bore controls fluid flow at the fluid control input of the variable cam phaser, wherein the spool has a first end ( 19 ) and a second end, ( 21 ) wherein an area of the second end ( 21 ) is greater than an area of the first end ( 19 ); and b) an internal differential pressure control system comprising a solenoid valve ( 15 ) comprising an electrical input, which controls a flow of pressure to the spool, and a pressure output ( 14 ) coupled to the second end ( 21 ) of the spool; wherein an electrical signal at the electrical input causes a change in the pressure output being fed to the second spool end, causing the spool to move axially in the bore.