Patent ID: 6792902
Filing Date: 2004-09-21
Classification: F01L

Abstract:
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 potion 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 cain timing system comprising:a spool valve (192) comprising a spool slidably mounted with a first end connected to a hydraulic fluid supply (236) and a second end being a differential pressure control system (DPCS) (234), where the DPCS (234) comprises a hydraulic piston, influenced by the amount of hydraulic fluid pressure from the hydraulic fluid supply (236), with a surface area that is twice the amount of surface area of the spool valve (192) it presses against, wherein the spool, being centrally located within the inner portion of the variable cam phaser, such that the axial movement of the spool controls fluid flow at the fluid control input of the variable cain phaser; a pulse width modulated (PWM) valve (206) having an electrical input and a sensor coupled to the spool such that an electrical signal at the electrical input causes axial movement of the spool; a position sensor (300) coupled to the piston of the DPCS (234), having a position signal output representing the physical position of the spool within the spool valve (192); VCT phase measurement sensors (20)(21) coupled to the crankshaft and the at least one camshaft controlled by the variable cam timing system; a VCT control circuit comprising: a cam phase input coupled to the VCT phase measurement sensors; a phase set point input for accepting a signal representing a desired relative phase of the camshaft and crankshaft; a spool valve position input coupled to the piston of the DPCS (234); a signal processing circuit accepting signals from the phase set point input, the cam phase input, and the spool valve position input, such that when a phase set point signal is applied at the phase set point input, the control circuit provides an adjusted duty cycle (320) for the pulse width modulated valve (206), which influences the DPCS (234) to move the spool within the spool valve (192) to control the variable cam phaser to shift the phase of the camshaft as selected by the phase set point signal.