Vct system having closed loop control employing spool valve actuated by

Abstract

A camshaft (26) has a vane (60) secured to an end thereof for non-oscillag rotation therewith. The camshaft also carries a sprocket (32) which can rotate with the camshaft but which is oscillatable with respect to the camshaft. The vane has opposed lobes 60a, 60b) which are received in opposed recesses (32a, 32b), respectively, of the sprocket. The recesses have greater circumferential extent than the lobes to permit the vane and sprocket to oscillate with respect to one another, and thereby permit the camshaft to change in phase relative to a crankshaft whose phase relative to the sprocket is fixed by virtue of a chain drive extending therebetween. The camshaft experiences pulses during its normal operation, and these pulses are used to change its phase with respect to the crankshaft. The camshaft is permitted to change only in a given direction, either to advance or retard, by selectively blocking or permitting the flow of hydraulic fluid, preferably engine oil, through the return lines (94, 96) from the recesses by using a stepper motor (134). The stepper motor serves to control the position of a spool (100) within a valve body (98) of a control valve in response to a signal indicative of an engine operating condition determined from a closed loop feedback system (108) which utilizes a predetermined set point, r (35), to dictate the desired camshaft phase angle to effectuate certain engine performance criteria.